"Core 2 Duo E6300 1.8 GHz (OC at 3.0 GHz) / Zigmatek HDT S1283 CPU Cooler / Gigabyte GA 965P-DS3 Motherboard / 2x1 GB DDR2 800 RAM / 2x160 GB Seagate HDDs / SilverStone ST50F 500W PSU / HIS IceQ 4 HD 4850 512 MB DDR3 / 17" LG Monitor"
That's all my specs (PC).
OC mean Over Clocking, basically it mean push your Central Processing Unit (CPU) by raising it's frequency, but every CPU has their own limit, my CPU is E6300 same like yours and i can OC it from 1.8GHz to 2.7GHz with only raising the frequency.
But, you can get higher speed if you raise the Vcore (CPU voltage), you can see that my CPU is overclocked at 3.0GHz (this with raising the Vcore a little bit).
Higher Vcore means higher heat than before, so with an aftermarket CPU cooler usually gives you more lower temps of cpu. Well, these all depend on your ambient (room) temps...