Core 2 Optiplexes vary because they made then for quite a while. You can get them for almost nothibg, but no telling what you will have.
Here's a rundown of them
Opti 745 P4 era, can run 266fsb 65nm C2D and Quads, OC option 130W QX6800 SLACP and Throttlestop software about 3.45GHz.
8GB DDR2 800...