Suggestion for cpu upgrade


2007 was a great year.
So I have an Intel Core 2 Duo E6750 (2.66 Ghz). I was able to oc it to 3.0 w/o affecting the memory bus @ all. I have an after market hsf on it & have been considering upgrading to a quad core. Heres the thing: I can only do Core 2 Quad (mobo cant support anything above that). Any suggestions on a great quad core cpu?