for me, im not that expert.. but since im free i try to tackle ur question

to me, NO NEED OC with m15x. m15x proc is more than enuf for gaming and all those usage. its super good. core i7 man, cmon no play play.
gaming depends on ur graphics mostly.,
starcraft 2 and diablo 3 IS MORE THAN Enough . im sure u can set max settings to ur m15x and play nicely. both these games are targeted to mostly med end computers. not target to high end computers as what crysis company did.
and u max ur specs for m15x, im sure can last a good 3 years. that is for me la. for me will really last. the specs are very good already.
but m11x, i think can last for 1 to 1.5 years only. later games sure cannot be played on high settings with this machine.
and bear in mind, games mostly depends on graphics, don have to oc ur proc if not really good at it.. don take the risk

"that is my opinion.. hope no one gets offended by it

"
hehe..
if i have money i sure got for m15x..