Try to disable hyperthreading. I think pb2 only uses one core, and hyperthreading divides the core in two so you're essentially playing pb2 with only a 1-1.4ghz single core cpu.
You say that you lag even with good fps because your PPS goes down. What makes you sure that it isn't an internet issue? Are you using a wire, do other multiplayer games run smoothly etc.? You could do a
pingtest and make sure that it isn't the internet's fault, although that test might not be that accurate.
Spikes can be caused by
- programs running in the background, although you've got 7 other threads for those so it might not be this
- other people using the same internet connection
- overheating (I guess)
Your computer might be overheating because of the unlimited fps, although I doubt that's the case, it's still good to limit the fps in order to have a longer battery life
and make the cpu live longer.
Edit: That cpu might have an integrated gpu as well, but I'm not sure. If it does, make sure that you're using the nvidia gpu, not the intel one while playing.