With that specification, why do you want to overclock? With my current setup, i can play Crysis at HIGH settings without lags. It depends though on your reasons why you want to overclock.
Intel's e7300 easily overclocks up to 50% core clock. just for you info. 
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E7300 | Gigabyte Volar | Asus P5QL PRO | 4 x 1GB Team Extreem Dark DDR2 800 | Palit 9600GT Sonic 1GB DDR3 | HEC Raptor 500W | 120GB, 320GB, 200GB SATA HDD | 20x LiteOn DVDWR | Viewsonic 19" Wide
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