skDoger :
ksham :
What games are you playing? It's unlikely that the i3 is bottlenecking the GTX 1050 unless the i3 is not strong enough for the games that you play.
To answer your topic question, the i5-750 is probably the way to go.
I usually play Rocket Leauge and War Thunder. Thanks for your suggestion.
It's super unlikely you are being bottlenecked with an i3 550 in RL unless the reqs shot up since I played. Nonetheless I would look at an i7 920 at least, not an i5. It's 2017 and 4 cores will soon be the low end. Your CPU is stuck being Nehalem based due to mobo, so you're suffering right now from a lack of IPC primarily... the extra SMT cores from Hyperthreading will help there and likely not cost you more because you're shopping for a very old chip. SB was a 20% IPC boost then Ivy and Haswell 10% each then Broadwell, and Skylake about 7% each (Kaby is a clone).
This puts your CPU about where a modern 2 Ghz dual core i3 is. 2Ghz+20%=2.2+10%=2.42+10%=2.68+7%=2.86+7%=3.06 which is 130mhz off your chip. Counting back from 3.2 instead of forward from 2 will give similar results.
Not bottlenecking, but definitely a little low end for a 1050. I wouldn't try it over 1080p on much and would look at.