GTA 4 is a real resource hog...even a GTX680 won't be able to squeeze more than around 50FPS from what I've noticed..so don't count your 7850 to squeeze a lot of FPS on GTA4.
However on BF3, I'm running an X4 955 @ 3.8Ghz (Basically the same CPU you have, just a bit faster due to overclock) and a GTX560 Ti. I get an average of around 50FPS on Ultra settings at 1920x1080 single player, and about 40-50FPS average on High settings at 1080p on Multiplayer.
On BF3, single player won't benefit too much from the CPU, but from your graphics (that 7850 will do great). On multiplayer, you'll experience much more performance if you have a better CPU, however, it's not exactly necessary to upgrade your CPU just to play BF3 multiplayer. And to be honest, I'm very satisfied with the FPS I get on BF3.
As for bottlenecking, your CPU won't bottleneck your GPU.
However for your RAM, you shouldn't worry one bit. You won't see too much performance hit if you're still using DDR2 instead of DDR3 RAM, and you won't see too much of a difference if you upgrade to DDR3 as well.