BF3 is very taxing even on a quad core so I doubt even if you O.C.'d your dual core that it would be able to keep up.Your gonna have to buy a new CPU.Of course that also means you need a new mobo and new RAM to go with it.
Your PSU is fine but your going to need a new graphics card.Espically if you want to take advantage of BF3's DX11.
Are you not buying anything or do you just not have a set budget(sky's the limit?)?