I just finished an upgrade from 7 to 8.1. Assuming you can get 8.1 drivers for all of your hardware I would recommend 8.1. Performance seems snappier to me (this may be attributable to a boot/applications SSD drive). I've had no issues with 8.1 and you can have it boot up to bypass the Start Page (the Metro Tiles) into the more conventional desktop look. This is what I do although I do have all of my primary DAW application pinned to the Start Page if that is where I may be - this is in addition to having them pinned to the Taskbar (I've done this since XP). I also have a custom Tool Bar that has links to all of my help files and the stand alone versions of various VSTs (Battery, Kontakt, Guitar Rig, Melodyne etc). This is very easy to do.
 
I recommend going with 8.1 because, assuming there are no driver issues, if you go with 7 you are pretty much building in a lesser life span...I can't recall when 7 came out but I'm guessing about 5 years ago...at some point in time MS will deprecate the OS.
 
Regards,

You also can add this $4.99 program to Win 8 to add the menu tree in desktop mode.  They also have another cheap program to resize the Metro tiles to run on the desktop.  They are rock solid.
 
http://www.stardock.com/products/start8/
 
 

I kind of echo most of the above.
 
1) Your hardware HAS to have 8.1 drivers! If not, stay on 7. For me, until my hardware gives out, I don't leave Win7.
2) For most folks with good hardware, your aren't seeing "major" improvement between 7 and 8. So if you have an open Win7 license and are tight on cash...
3) It will be a long time before Win7 is sunsetted. Probably 5 years minimum.
 

FCCfirstclass
You also can add this $4.99 program to Win 8 to add the menu tree in desktop mode.  They also have another cheap program to resize the Metro tiles to run on the desktop.  They are rock solid.
 
http://www.stardock.com/products/start8/ 

You don't need this with 8.1, you can now get your start button back, which will bring up the ModernUI screen, here you can put on shortcuts to all of you apps... it works well... In a lot of cases this functionality is hidden by default and needs to be enabled.

I ran 7 on an Acer in the studio ever since 7 was released. All the talk about 8 made me leary when it came time for a new machine. I bought a Toshiba with 8 on it, loaded up X3 64 bit, and I was awestruck at how much better the experience was with X3. Then 8.1 update came along and all the talk made me leary about updating. I finally bit the bullet and updated to 8.1. The only problem I had was my Addictive Drums and Addictive Keys registrations went amuck! I had to go to XLNs website and remove the registration, give a new computer name, and run the installer. Once the installer ran, it scanned all the Xln folders and prompted me that everything was up to date. Other than that I can't say enough good about my experiences with 8 or 8.1.
BTW, 8.1 put back the Start button on the desktop! I sure did miss that booger! At any rate my experiences have been excellent and I would highly recommend that you consider going to 8.1! If for no other reason, you know how this works. If you don't upgrade then in 4 or 5 years 7 will no longer be supported and you will have to jump to Windows version 22.3! I skipped Vista because so many people said it was a dog. When I got 7 I wondered what all the hub-bub was about. Hope this helps.

Sid, so do you have X3 on both? Or does just the newer one have it?

Yes, I have X3 on both the Asus and the new Toshiba. The Toshiba is a laptop and it eats the Asus desktop alive! The Asus is Windows 7 and the Toshiba is 8.1. Check my signature for specs. No, none of my computers are custom built. They are off the shelf but I have stripped out all the bloatware. The Toshiba is working out well with the two Roland Studio-Capture interfaces linked together. That gives me an ultra compact remote recording rig with 24 built in mic pres with low impedance jacks with built in compression on each channel. The rest of the inputs are tip ring sleeve inputs for a total of 32 ins and 20 outs.
 I have not done all 32 tracks in realtime yet. I have done a few church choirs with the 24 channels and the Toshiba never even stuttered.

apples/oranges Toshiba i7 vs asus i5/hp i5
 
Would really LOVE TO HEAR some real world experience on the OPs main question:
 

jtbarr
 
Here's the issues I would like some QUANTITATIVE data on:
 
Assuming 64 bit versions of both.
 
1.  Is the multi-core scheduling any better under Win 8?  (vs Win 7 with latest Service pack)
 
2.  Is the system timing any more accurate with Win 8?  I heard there are MIDI jitter problems in Win 7.  I haven't measured it, but is it MIDI only or is audio affected?  I have noticed latency problems in my system with Sonar 7 and X1 (I now am using X3), but usually these latencies were ASIO related or other system problems.
 
 

 
I have had win 8 for a long time and haven't installed it.  Now have moved to a i7 4930 6 core/12 thread sweetheart of a cpu and still notice periodic redlining of core/thread #1 on complex creations while load is light across the board... Throwing way more at it than at my old i7 950, but still would love to see a better distribution...given ooooodles of stuff is going on that could be spun off to the other 11 threads I would think (me not necessarily a braniac)
 
THAT IS THE MAIN ISSUE, to little old me...
seems easy to quantify but...nadda yet.

microapp
MS supposedly wrote W8 from the ground up and dumped all the legacy code.

For any new OS release (for any mature OS) the vendor never rewrites more than 1/10000000th of the code.  There might be certain modules that are scrapped and completely rewritten, but 99.999999% of the code transfers from one version to eh next.  Sometimes parts of the OS might be processed with new compiler options, e.g. to adopt 64-bit mode.  And some changes are so sweeping that hundreds (if not thousands) of modules might require some touch-up to remain functional.
 
Windows is estimated at 50 million lines of code.  Trust me, you wouldn't want any OS that had 50 million new lines of code.

I can say as far as the OP that I am getting a higher count of plugins without clicks and pops with 8.1 than I ever do with Windows 7 and X3. Also, I have not done any tweaking to the settings in either of these computers. Some forums say do it, some say don't. I just never got around to it. Anyone in here using 8.1 that has improved performance with any tweaks?