mettelus
FWIW, I wouldn't go toe-to-toe with Jim about system performance, is best to just sit back and read his posts. 

It's not about that...   
I've been using Win8.1x64 for a good long while.  It's a fine DAW platform.
If you use a multi-touch monitor (or want that ability), you have to go with Win8.1x64.
 
You don't really gain (or lose) much either way... 
 
Within the next couple of days, I'll post some up-to-the-minute numbers on a new Z97 based machine.

Well if you want to go deep, i think cakewalk covered this a while back:
http://blog.cakewalk.com/windows-8-a-benchmark-for-music-production-applications/
 
BUT being a system builder myself (to the point i have my own programmed/tune BIOS and Firmware) i think mostly you guys are not covering the most important aspects.
 
First there´s hardware then drivers, what´s the point of going for a OS version where your usb or lan or whatever will cause spikes of 2000 dpc. 
If you want the best OS for you just install both and try, disable all the hardware you don´t need open a LatencyMon and check your DPC, then start to fine tune both, first doing BIOS changes, then OS changes (energy, core parking, timers, disabling services, etc).
Play with different driver versions for the hardware you DO need, if it´s a laptop disable the battery acpi device, try software like throttlestop to lock CPU speed, etc etc
Soon you will be able to know which OS gives a more stable low DPC, go for that one.
 
Often the results are not BECAUSE of the OS but because of drivers/hardware for that OS.
Example: My Intel LAN performs perfect in Windows 7 with latest Intel drivers, but does monster DPC spikes with latest Intel Windows 8 drivers, solution = using the built in Windows 8 drivers... this type of stuff is something you must test out and find out. 
 
I can get 96Khz 24bits with 128 buffer (4.9ms) (unfortunately my audiocard does not allow 64 buffer @ 96Khz) and load 3x full 8 channel omnisphere + 3x absynth + 3x reaktor + 3x waves codex + 3x waves element + 3x superior drummer add guitar rig and izotope mastering in ALL tracks and not a bump in audio... BUT only because i had to fine tune the system. If i load a clean image of Windows 8.1 or Windows 7 without no tune up it will crack and pop like crazy.
 
So i would concern myself mostly with hardware, as i said before in other posts, latest laptops with nvidia for instance will give a minimal DPC latency of 600 (even with power features off)... same unit with AMD gets 70... think about that. And then test both OS version and it´s drivers on both OSes.
Probably latest gen hardware will start having better driver support with Windows 8.1... probably...

For what its worth (I is an old guy), my "experience" with Win 8.1 was beyond frustrating!
I own it, it sits on a WD Black 500gb drive that I use alternately as a doorstop or coaster!
(You think I'm kidding right? NO, I am not kidding!)
You own (actually, read the EULA, you are "renting" Win 7) that's where I would stay!
And why, oh why, would anyone "argue" performance with Jim???
Do we think he pulls these things out of his arse?
Just sayin'...
T
 
 

Wa wa wait... Regarding hardware performance under Win7 and Win8 can vary.  A given interface might work better with a driver  written for Win8 as opposed to one for Win7 and vice versa.  This is very subjective, but a real factor nonetheless.
 
As for the upgrade question, Reece, dishing the cash may not be wise unless you found a really good deal.  After all, Win10 will be released later next year, but pushed back three or four times for actual release in 2017, maybe even 2018.  Win7 will hold up well since there is no indication that MS plans on ending support to date.  

fireberd
There are reports that the new Windows 10 will be a free upgrade for Windows 8.1 users...

Now, as for the 8.1 upgrade to 10, I was of the understanding that Win9 (now renamed to ??) will be the free update.  Yet, I have read a blurb stating that MS may consider a free upgrade to Win10 as a marketing scheme in order to win over customers by encouraging the purchase of Win8 now and gain Win10 later without additional cost.  I am not certain that that is actually the case since I have not read anything from MS in that respect.
 
Eh, whatta I know.
 
Kind regards,
 
Living Room Rocker

lol, well, I decided not to upgrade  and I've started building the system on win7 again.
 
not gotten very far - but I've made the decision to stick with win7 for now!

FWIW, I finally got around to installing the Win 10 Beta.  I'm not impressed.  The Beta is basically Win 8.1 with some (poor) changes to the start menu in the desktop.  I'll be loading Sonar X3 and installing the driver for my Roland Studio-Capture on it in the next week or so (when I have time) to see how it works.  Since Sonar X3, in Win 8.1, works equal with my Win 7 installation I don't see the Win 10 Beta being any different. 
 
I will concede that the Win 10 is a Beta version and what ultimately comes out as the final version may be a lot different. 
 
There are already users on the Windows 10 forum that have changed the start menu to either Start8 or manually edited it to look like Win 7.