Throwing 250-300 mhash/s
Is that with a HD 5850 ?
yes, I'd either be mining or doing other stuff so overall electrical usage is negligible.
My HD5850 started stock at 260mh/s and is now running at 391mh/s

Oc it !
Out of curiosity - how did you get the 5850 to 391MH/s? What's the voltage and GPU frequencies? And what software do you use and how many watts does it use?
I've found mine to be quite stable when undervoltaged to 0.975-0.987 and GPU at 775-785MHz (which results in 305-308MH/s). On the good side - power usage is pretty decent - 675W with 5 of them mining.