You probably wont see any noticeable difference in fps. The x3470 and the i5 750 are both going to have very similar performance. While the x3470 does have hyper threading, PUBG does not scale well with more cores. PUBG runs better with fast single threads. The slightly higher clockspeed will be the only benefit, but its not going to help much.
You would probably do better by getting 4gb more of RAM as 4 is really the minimum for Windows these days. But honestly, you are running on a platform that is nearly 10 years old. I would save up some money and get into something more modern. Even a G4560 would be a big improvement over what you currently have.
So if you get the x3470, I would not pay much for it.