Getting anything over a 955 ($110) in the phenom II x4 line is a waste of money, you can easily crank the multiplier to x18 to equal a 975, and if you're lucky a 980 aswell without any extra voltage. For gaming the x4's are actually better than thuban, so go for that if you just can't wait. Make sure you go for a AM3+ mobo as hopefully AMD can un-f*ck bulldozer somehow with a stepping, and continue using AM3+.
And no you can't overclock to 4ghz on the stock fan.
Never heard about 760g supporting AM3+, I thought only some 890fx and 870 mobo's were able to be made compatible though a BIOS update, I'd go the safe route and get the cheapest 990fx you can find, plus you won't want to be missing SATA III and USB 3.0.