Now that I'm used to the game I'm having a lot more fun.
...also the helicopter changes have made my life was a gunner/pilot easier.
I'm partial to the 870 on every map that isn't wide open, also. It freakin' destroys people.
Also m4, you might need more power. My buddy has the same setup you do, except his runs a 950w. He was having some stability issues until he upgraded, too. I mean, technically 750 should be fine, but it seems to be a trend with these cards.
Also you shouldn't be having heat issues. I run a 6970 and it is pretty cool. I have three case fans blowing on it, though.