get the CPU and also dont buy a 120hz monitor buy a 240 for the rig that you have you will want the better monitor
240hz? Those don't exist for gaming. Don't confuse TV tech with PC tech. A 240hz TV is still a 60hz monitor when a PC is connected to it, they can't except more than 60hz of input.
The highest hz monitor I've seen is 144hz. ASUS VG278HE, which is also 3D Vision 2 capable but without a built in kit.
I also agree, that CPU is pretty slow and will hamper your ability to enjoy a 120hz monitor.