YEP Thought this was worth mentioning, because this was driving me crazy for quite sometime and I'm not even close to being a Newbie, this current computer/workstation being my 6th generation build and configuration since 1999.
 I didn't have a clue my problems were coming from my beloved and rather old PCR 500 MIDI Keyboard Controller until disconnecting it to make room on the desk for a new Behringer X Touch DAW controller.
 Not only does SPLAT load up and load projects much faster, it hasn't frozen up and stopped responding during long and rather large "mixing sessions" with high track counts of over 30 to 40+ tracks. I had never had any recording session issues, I can input 16 audio tracks at once along with recording several MIDI tracks without any issues other then band members breaking down from exhaustion. It doesn't happen frequently, but it does happen.
 
 Of course SPLAT never really started up or loaded projects all that slowly, never had any recording latency issues so I never noticed there was a problem until I noticed how much FASTER it would seeming blaze in to up and running. 
 Also using so much processing with so many plugins and VSTi instruments on so many tracks I knew these projects where being extremely resource intensive especially recording at 24/96 without freezing any tracks at times, I hardly could blame fault to anyone but myself and blew it off as more of an inconvenience then an actual problem.
 And not even once ever even considered the possibility of a MIDI Keyboard Controller creating these types of what I consider audio processing issues.
 That's why I was kinda shocked at such a noticeable performance boost I'm experiencing by simply removing the PCR 500 from my system, which BTW still works great plugged into my Mac controlling Reason.
 I also haven't experienced any freezes in SPLAT in almost 2 months since installing the X Touch which I'm thinking is getting to be a little long to chalk off as coincidence. 

Have you used PCR just as a MIDI keyboard or as a controller as well?
In the later case, which Control Surface plug-in was you using with it?
 
Which drivers was in use and was the firmware updated?
 
Sorry I am asking all these question. I do not even have the device. But I collect all the information available, to occasionally help other solving Control Surfaces related problems. F.e. I know how to crash Sonar with X-Touch, how to slow it down with some Control surfaces, etc. But most important, I have found workarounds for all problems I already know

I used to have a PCR500, until Windows 10.  The Roland PCR drivers had to be hacked to work with Win 10.  Initially the hack worked but later Win 10 upgrades had to be further hacked to make it work.  Maybe that is the problem.
 
My PCR500 was sold to a person that was still on Win 7 so it worked OK for him.

I was using the PCR 500 as both a very basic DAW controller for SONAR; transport controls, faders/gain, and rotaries as pan pots, and created several MIDI maps for controlling synths both software such as N.I.'s Absynth and B 2 and integrating some of my favorite vintage hardware gear that supports MIDI control Program and Control Change messages like the Roland Super JV 1080 synth mod., PMA 5 synth mod./sequencer, Kawai K11 digital synth to rackmount multi effects processors which are great for live shows, insert processing for recording and or separate monitor send mixes for headphones.
 That's how we did it back when we were running SONAR 4 PE on a Pentium 4 powered by Windows 2000 with a 128 mb of memory.
 One of the things that really attracted me to the PCR 500 was the fact it could be used as a stand alone MIDI controller simply by using an external power supply and not just USB buss powered, and it stores 8 "User Defined" MIDI Maps internally that can loaded by the push of a button A2 through A9.
 All MIDI map programming, creating, and storing was done with the PCR Editor Librarian, with either dynamic mapping and or digging into 1000's of pages vendor manuals and help files in search of vendor specific proprietary continuous control and program changes.
 Never even actually trying SONAR'S ACT because the PCR's dynamic mapping button is so handy
 
 My PCR stopped connecting thru USB with the Win 10 upgrade as well, all I did was log in as Admin. and roll back ( I did NOT uninstall) from Device Manager (I did not hack the PCR driver installer) just did a roll back to an old Vista version I had stored on CD and forced it to load over the newer version. and all has been well through every Windows update.
 What I actually did was put the PCR drivers on a personal "exception list" in Windows Registry by signing off on protection from anything that not on Windows Digital Signage List. Windows will not load any driver that's not on the list upon boot.
 
 This is of course a very risky approach and I'd be willing to bet it can only be done with Win 10 Pro and don't really recommend it. I most likely wouldn't have done if I wasn't sure it would work after testing the PCR routed thru standard 5 pin MIDI ports first, as opposed to connecting thru USB port.
 This is where the external power supply come in handy. Windows might be able to shut down power to the PCR's USB port, but it can't do it thru the 5 pin MIDI cables routed thru my MIDISPORT 8X8 USB patch bay, LoL.
 Roland can fix this problem simply by certifying the PCR's USB drivers package, but why should they support something this old for free when they'd much prefer to sell us a new one to stay in business??
 
I never updated the firmware in the PCR, my motto is, if it ain't broke I ain't fix'in it, and I have experienced and witnessed times when firmware updates effect "User Defined" MIDI Maps in a very bad way rendering them at best "useless" by no longer working at all, to crashing the entire system because the protocol or some parameter has changed for an improvement nobody asked for. 
 I just spent way too much time sifting thru MIDI implementation charts and GM spec charts creating a whole Documents folder including a copy of the firmware version installed, and of many MIDI maps to get the PCR to do what I want and how I want it to do it.
 And being I still have all that vintage gear, plus Reason and other synths installed on the Mac I'm still lov'in my PCR 500, which as any and all MIDI Keyboard Controllers go, are far better then mixing with a mouse just for the sake of controlling more then one track at a time pretty much ill suited for precise DAW control for automated mixing because the faders and nobs don't latch, not to mention being in very uncomfortable position where your only arm rest is the keyboard, and the keyboard is running live controlling something like Rapture Pro or worse perhaps Novation Bass Station can be very startling when your tired wrists accidently brush up against D# during a tricky fade.
 

Thank you for the detailed explanation of your setup!

Steev, I didn't want to hack anything in Windows 10 so I just gave up on the PC500.  I never used it much anyway so no big loss. 

fireberd
Steev, I didn't want to hack anything in Windows 10 so I just gave up on the PC500.

I just want to mention explicitly, that the procedure to make Roland Win 8.1 drivers to install on Win 10 is as "hacking" as adding one more guitar track to a project is "mastering"...
 
The driver is not modified, its signature is not broken and the behavior after the installation is exactly the same as it will be with dedicated win 10 drivers. So no way the procedure can be called "hacking".
 
Roland has explicitly hardcoded that INSTALLER should not work in ANY future Win version. Discarding this one text line in the INSTALLER DESCRIPTION breaks this description (text file) signature, so Windows should be told to ignore the fact (again, during installation only, the driver itself is still properly signed). I still wonder why no lawyer in US has tried to win against Roland for that... it is like hard-coding into a car engine that it should stop working once you cross particular US state border, without mentioning that when selling the car...
 

I had the PCR500 working, initially in Win 10.  After the annual update it no longer worked.  I remember seeing what had to be done.  I'm a computer tech but was still having issues.   I was one of the early adopters of the driver hack to get Roland devices working in Win 10.  I had a Roland Octa-Capture and hacked the driver to get it working when Win 10 came out as Roland didn't have Win 10 drivers ready, even though they had a year or two to do it.
 
I rarely used the PCR 500 so it wasn't a big deal.  I only had it as I bought it cheap when Guitar Center was "blowing out" the discontinued PCR line.  I had a Behringer BCF2000 at the time so I didn't need/use it as a control surface.  With the low initial cost,  I got what I paid for it when I sold it.