you can overclock radeons a a fair bit before thermals become an issue, the best advice is to be gentle with it(small bumps don't ramp up your voltage if you don't have to) you're also going to want to underclock the memory(it'll help keep power usage in check and won't affect hashrate) i dno't have experience with the 7870 to give you any targets but if you look at the mining hardware comparison on the wiki it'll give you some ideas.
he's using "khash" so i'm assuming he's mining scrypt. if that's the case, he shouldn't underclock memory because that will decrease performance. but scrypt is not very profitable and the volatility is way too high, so I recommend mining bitcoin (lower power usage, lower temps, steady income).i've been gone so long i assumed that was a typo XD litecoin uses scrypt right? (this is probably where i regret destroying something like 1k ltc)
