Home Premium is awesome, you won't have any problem with the visual themes....
No, Gaming does not take a performance hit, it does better... Games like BF2142(when it lets me login, EA's Account Server's fault), B&W2, CoH, TDU, and Steam games, just seem to work smoother. Vista boots faster than old crappy XP too. I love Vista!! Just some printer driver problems, but that's expected and not MS's fault.