What model Optiplex and what size? Upgrading the cpu on business computers is not a good idea. Try maxing out ram or get a bigger hard drive first. Upgrading the CPU does not make a lot of difference in performance.

i7-3770.

you have an OptiPlex 7010

https://www.dell.com/downloads/global/products/optix/en/optiplex_7010_technical_guidebook.pdf

According to game-debate , you'll have 24% better performance switching to an I7-3770 if your PC is one of the chassis sizes that can take it.  That's hardly noticeable.  It also translates to 1.24x faster.  When I upgraded CPU's in a previous PC, I hardly noticed the difference at 64% better performance.  Sometimes performance change is marginal going from quad core to quad core.

Backing what xps630 said, (which I thougnt was in this thread) and it's what I did, you'll notice more of a difference switching to an SSD, then RAM if you still want to go faster.  Then CPU if by chance still not satisfied.