oc gpu easy cuz u have the tools for them
like ati tool and rthdibl etc etc

but high end cards oc are stupid
the best is if u want a simple gc for a simple pc but just wanna do mild gaming, get a low/mid end card oc'ed already
like Palit/XpertVision Sonic series
they are oc'ed by the engineers
but u can oc them further
e.g. 7300gt Sonic
stock - 500/1000mhz
after oc can reach - 680/1690mhz
link - http://reviews.sc3n3.com/review.php?review=2&page=14
i dunno how they got there on the stock fan but its actually the speed of 7600gt (except with 4 fewer pipes)
haha