Dell OptiPlex 9020 CPU Upgrade! What CPU???

I've had this Optiplex for about a year now and it doesnt run games well. I cant play fortnite on lowest graphics. I found out its cpu. I have a old Intel i7 4770 3.40GHz or 3.39 or 3.38, i dont know because task manager says speed 3.38GHz and the name says 3.40GHz. I want to know what cpu i can get to improve performance on games. Because after upgrading my gpu from a GT 1030 2GB to a Intel Arc A380 6GB, i barely got any better fps in games. And it runs really well. Low vram usage on games. I tried to optimize my cpu and already see performance improvement. But i cant overclock the cpu because of how old it is. So im thinking a cpu upgrade.

Dell Optiplex 9020 SFF

GPU Intel Arc A380

Ram/Memory 16GB DDR3 1600MHz

Disk SSD 512 GB