Too be honest.
3GHz is perfectly good enough on BF3 which is not all that CPU intensive game. With the exception to the 64player maps. You may see slight improvements. But not enough to warrant the price of the new processor.
You should reach medium atleast even before the new CPU.
my 560 with athlon x2 can not play any settings. I get 40 fps to 15 fps, very rapid spiking. fps is always the same no matter from ultra to low. In BF3 you can type a console command "render.perfoverlayvisible 1" and it will show you cpu and gpu usage. It is my cpu, always fully loaded, my gpu never gets the chance to go past 50 percent load.