Sorry for bumping this old thread, but I'd rather share my experience on this topic here, than to re-post the same topic.
I've ran the basic benchmark (Windows Experience Index) 3x for both Windows 7 and Windows 8/8.1, and here are my results:
CPU 7.6, RAM 7.6, Graphics 6.9, Gaming Graphics 6.9, HDD 5.9
CPU 7.5, RAM 7.6, Graphics 6.8, Gaming Graphics 6.8, HDD 5.9
I've also ran the same basic benchmark on another machine, and here are my results:
CPU 6.4, RAM 6.0, Graphics 6.7, Gaming Graphics 6.7, HDD 5.9
CPU 6.3, RAM 6.0, Graphics 6.5, Gaming Graphics 6.7, HDD 5.9
While the difference aren't huge, Windows 8/8.1 appears to be lagging a bit by a hair.
I also like Windows 8, especially the 8.1 update. I like the new modest metro look compared to Windows 7's aero or even basic. I also like the functionalities and new features, but when it comes to gaming, every little performance gain counts from switching themes, custom start-ups, etc.
My solution is to dual-boot. And if this is not an option (say, you can only buy one OS), then base it on personal priority whether gaming is really the main focus or not. And as far as longevity, Windows 7 will be supported by Microsoft up to 2020, which I'm sure third party developers will do so as well for a long time. Just look at XP...
Besides, many agree on the following:
Not so good Windows: 98, ME, Vista, 8
Pretty good Windows: NT, 2000, XP, 7
Also, Microsoft themeselves have stated that Windows 8 is optimized mainly for mobile devices with touch screen, while Windows 7 is still the preferred desktop OS.
Microsoft support, forums, google searches, discussions, tech support, wiki.