I doubt it. Windows 8 was important for AMD mainly, and those who run more than four cores. Windows 7 simply didn't get it but I can't see any performance boosts coming given it's running on the 8.1 shell.
Mind you, those who are still on 7 will get a nice boost and won't have to bugger around with core parking or any of the other hacks.
I saw quite huge gains in CPU intensive games when switching from 7 to 8 on my FX 8320. I got 15% higher score in 3dmark.