JWink
For the sake of argument, let's assume that I do in fact need my buffer at 512. The limiting factor seems to be my Cinematic Strings 2 library which causes glitches on fast runs if I set it any lower, even though it's on my fastest drive (an SSD).
 
Why am I seeing such noticeably poorer performance in Sonar than in Cubase under otherwise identical hardware settings and plug-ins? The only difference is that the tracks in Sonar have the ProChannel engaged.
 

Here's a couple of thoughts, and I use Cubase 7.5 as wells as sonar x3/platinum.  Some things seem better in either program - this is not a case where I've seen a noticeable difference.  
Enable cubase's version of the prochannel (the channel strip) with similar settings to sonar and see how it impacts your performance.  
Some things happen under the hood in cubase that you can control in sonar.  Some ideas - 
in preferences, select audio/config file and set extrapluginbufs to 32
 
In kontakt, if you have the ram, under options/memory increase the instrument preload buffer size.  This should definitely help with cinematic strings - it certainly helps my spitfire libraries when I'm using many of them. 

Thanks guys!
 
Playing around with the various suggestions here, I've found that there are a few things that I can do that improves Sonar's response by about 12-15 msec, which is enough to make it playable again (though still not as good as Cubase!). Bypassing or deleting ALL effects (incl. ProChannel) will do it, and disabling PDC seems to work as well. For my orchestral template, I'm content with just using that when I'm sequencing.

jshep0102
I have a Jim Roseberry system (see my sig) and can run a half dozen instances of Kontakt running Kirk Hunter Strings, Chris Hein Horns, Omnisphere, Steven Slate Drums, Trilian, among others in Platinum. I can run at 32 samples with all of them frozen and feel no latency recording guitar through Axe Fx Ultra and listening via my monitors (not direct monitoring). My system is a 'few years old', too. Not sure if you're running fx like verb or other plugs that induce latency.

 I see an RME 9632 in your profile.  I think that makes a difference and it's a PCI device. 

I can run X3 or Platinum, 24 bit/44.1 KHz at 48 samples = 2.something milliseconds latency for soft synths or under 5ms for "round trip" latency when monitoring input audio through sonar, including using many fx plugins (so long as I avoid plugins that require delay compensation).

My previous UA-101 interface, which was pretty mainstream in terms of price, could manage round trip latency of 10ms without any problems. I've not needed to set latency higher than 256 samples in years.

As has been suggested, I suspect the long latency issue is down to PDC or a system not correctly optimised for Sonar, and freezing tracks might help as well.

Don't forget that ASIO Direct Monitoring thingy - Cubase support that, not sure about Sonar. And not sure about Presonus interface either - but something to check out maybe, both interface and daw need to support it.
 
It means audio can slip past any roundtrip inside daw, interface shortcut that for you.
So that is audio, not playing midi stuff which would need midi in and only audio out buffers delay.
 
Another note I made upgrading to Sonar 8 2010 or something, evaluating new interface for my new daw at the time.
 
I could run a demo project in Sonar, if it was 11 audio tracks, at 128 samples buffer - no crackles.
But inserting a synth, Dimension Pro, it crackled monitoring that at 128 samples - just playing a note.
Increasing buffer to 192 samples, DP played good too.
 
I created a fresh project, only one track with DP in it - same thing.
Need to increase to 192 - then fine.
 
So something is different in how Sonar insert samples from a virtual instrument. It seems to me like they need the full roundtrip delay to run a synth - that samples are sort of inserted where audio comes into daw and need an extra input buffer size to run without crackles. Or if midi is delayed one audio buffer or something - that could explain some issues running VST midi plugins in Sonar.
 
I ran the same thing in Reaper, and it work just fine at 128 samples playing DP.
 
So looked at delay this firewire interface reported - and if it was 90 out and 150 in, or similar. Very different in and out.
 
Skipped firewire, and now running internal RME HDSP 9632 card at 64 samples, no problem.
Ran Sonar 8.5, X3 and now 2015 - no problems.
 
Just something I noted at the time, don't know what to make of it.
It seemed that the different delays in and out were involved somehow on the firewire - combined with how Sonar insert synth samples.
 
Lesson learned - interface+drivers may make a big difference.
 

Pops and crackles...that was my nightmare with many firewire pci-e based setups in past!
 
I found some things help when tweaking a system for such setups is necessary.
 
cpu parking?...that would be one...tweak
 
I think it has something to do with PCi bus, and IRQ sharing..but that is my perspective point of view...ever since ever was.
 
So i would say turn off all redundant devices in your device manager..when wanting to do audio...and reboot into that...then go nuts!....lol
 
I would also turn off HDMI audio...could case issues as you describe at any latency settings...As I believe Sonar has a low video setting threshold...plain jane video or interference with boost or excelerators oh high......issues like crackling when (like certain movements with mouse over certain windows or plug in apps) causes on video onto audio interference...mouse curser/mouse drivers or memory allocation for/ and video card drivers/memory or something might be tied up some how?...those devices that merge in some way, seem to hinder some people performance, if not tweaked to perfection.
 
Best to get that sorted...disable what is not needed in device manager or control panel / and also setup your power management settings
 
..(HD Audio, more so the HDMI AUDIO, and other DEVICES  blu tooth , wi fi, and nics)
 
Then give it another bash....Might help?

Sir Lesinterface+drivers may make a big difference

A huge one. It's not made easier by many drivers not accurately reporting latency either. Often they miss out things like additional "safety buffers", sometimes the reported latency is simply wrong.

The only way to check round-trip latency is to loop a cable between an interface input and output, then use an audio track to send a "ping" to the output and record it being returned to the input, then calculate how long it took.

Or use a tool such as http://www.oblique-audio.com/free/rtlutility which does the work for you and makes it very quick and easy to compare performance at different buffer sizes and sampling rates.

Why am I seeing such noticeably poorer performance in Sonar than in Cubase under otherwise identical hardware settings and plug-ins? The only difference is that the tracks in Sonar have the ProChannel engaged.
 
 

I think this is the cause. 

tlw

Sir Lesinterface+drivers may make a big difference

A huge one. It's not made easier by many drivers not accurately reporting latency either. Often they miss out things like additional "safety buffers", sometimes the reported latency is simply wrong.

The only way to check round-trip latency is to loop a cable between an interface input and output, then use an audio track to send a "ping" to the output and record it being returned to the input, then calculate how long it took.

Or use a tool such as http://www.oblique-audio.com/free/rtlutility which does the work for you and makes it very quick and easy to compare performance at different buffer sizes and sampling rates.

Thanks for reminding me to do this. I found I was 38 samples out (ouch!).
I would add that after you've done it you should also do this for peace of mind with your new offset (use a clean sine wave, or better still a sawtooth you can line up):
http://forum.cakewalk.com/FindPost/2745971
 
 
I did both and both results agreed with each other...
 

EDIT: I'm stupid need to read before engaging the fingers :P