I don't see that much difference in Windows 7.
As I understand it... If a game is designed for DX9, Windows 7 will run it in DX9, and not 11. It was the same way in Vista.
I'm sure you've heard many people say that the sure way of increasing gaming performance is to turn Aero off. But this too is false, because as soon as your Video Overlay is triggered for Full Screen activities, Aero automatically gets disabled. Watching online Flash Videos like Hulu is a different matter, because Flash does not use Video Overlays.
I can however, recommend a few things to improve your performance for games. Most of these applies to all versions of windows.
1. Add more ram - for obvious reasons
2. Use V-Sync - This will force the game's frame rate into matching your screen's refresh rate. You don't need frames that you can't see due to slow refreshing of the built in screen. It also makes life a lot easier for your intel GMA(GPU).
3. Run games in Performace Mode(Power Management) - Intel's Atom features a speedstep technology that will lower the amount of power being used by the CPU on the fly, for increased battery life. But this can make your games run slower. Plug in the AC, and let 'er rip.
4. Disable TSRs(Terminal State Residents, those icons in the task bar) that use constant CPU time - This one is tricky. Not all background processes/TSRs use constant CPU time. So disabling them all is pointless. For example, iTunesHelper.exe only uses its Interrupt when iTunes is running. But others like uTorrent(minimized) will constantly suck 1%~5% of your CPU's time as long as its running. This can hinder your game's performance.
5. Close Firefox - Firefox is a memory hog. It can consume a gig or more of ram even when it's idle. On top of that, it will suck a couple percentages of your CPU's time while in idle. Close it down.
Hope this helps.