You’ll probably be able to game on this CPU for quite a while still.
I’m guessing you're talking about those 95W versus 125W ratings. That’s just the TDP, which basically tells you how much power it draws and how hot it's going to run. You aren't actually getting any extra performance out of a higher TDP.
Signed, I wouldn't waste my money on a 775 either; better to save up and grab something modern. You can snag some new Springfield processors for about $200, which are newer and way better than that old Q6600, plus they use a more recent socket...
Maybe you should've put more of that cash toward a decent GPU instead.
I mean, there's no way for me to know anything about your power supply if you don't even know what it is. That’s probably why I suggested those 4670/5670 cards; they can handle games just fine without needing an extra power connector, plus they draw way less juice anyway.
True, you're running DDR3. If there’s an open slot, you might as well grab another 2 or 4GB. Any random stick would probably work, I guess, but if you can find the same brand just to be safe, why not? You can always double-check the brand using CPU-Z