Well, i play at LGA775, wich has an E8400 dual core @ 3.0 Ghz.
I have an GTX 650 Ti Boost, i was running BF4 on lowest and my cpu was running 100% while the GPU was running 55-60%.
I did a little upgrade to a quad core and BF3 is running ultra @ 40-50 FPS.
What you should do is buy a second hand CPU, MOBO and GPU.
A RAM upgrade doesnt bump your FPS, it only makes your maps/levels load in faster. Look for a CPU + MOBO first and upgrade the GPU later.
Good luck!