Its not that bad, the single player bf3 will be fine but large multiplayer maps you will have to lower the settings. Planetside 2 I cannot find any post beta benchmarks but it is over the system requirements so will play it but I don't know on what settings.
I'm upgrading to a 3770k in the summer, but i don't have the money right now. My friends told me i would be fine.. Is there a cheep AMD solution that can run a large BF3 game, till i can upgrade again?
OC'ing on an OEM motherboard is likely not an option, though typically with ddr3 1333MHz, the system sweet spot for OC'ing would be 250MHz (x14 with your CPU).
The other issue which cpmes to mind: Did you also upgrade your power supply? An OEM PSU will not run a 670.
To be honest you would get EXACTLY the same performance in BF3 singleplayer with the Athlon and a Core i7.
The game really isn't CPU dependent.
Multiplayer is another story though.
In Multiplayer, you'll actually see a difference, if youre playing with more than 32 players.
Otherwise you'll get the same performance.