I plan to OC my E7400. Here is my configuration:

Intel C2D E7400 @ 2.8Ghz with Stock Cooler
Kingston DDR2 800Mhz Dual Channel 4GB RAM
Gigabyte EP45-UD3L Motherboard
1 x 640GB WD SATA HDD
1 x 1.5TB WD SATA HDD
1 x 2TB WD SATA HDD
1 x DVDWriter SATA
Sapphire HD4830 512MB DDR3 Graphic Card
Cooler Master Extreme Power Plus 500W Power supply

How much I can overclock with my CPU with stock cooler?

Please advise.

Thanks.