Okay guys, I really appreciate the quick replies but I'd like it if somebody could throw out a few names/model numbers of CPUs that could simply just be faster than the factory one.
I found this old thread
where the guy says he managed to get the smallest Optiplex 745 USFF model to be faster with a Q6600 SLACR at around 2.4 GHz.
Having read this I'm confident that there has to be something that can make my SFF model a bit faster than that but I need direction.
Please help with name/model suggestions as I am new to all this hardware upgrading stuff and don't know where to look first.