Post your BAT address, I wanna send you some guano sized thanks for this. I've been running my R9 280x with the exact same settings as you and was never able to break 550kH. That is, with one key difference... I never tried underclocking the gpu. You are right, on the R9 280x, that is KEY. My hash rate jumped instantly. Anyway, post or PM me your address and I'll send some bat poop your way. Seems like a weird way of saying thanks, but whatever.
As for the 7950, I think they average around 600-650kH without any major tweaking, with the ability to hit over 700kH if the sweet spot is found. With mine... Intensity, Thread Concurrency, and Mem clock made big differences as well as the mem clock to gpu clock ratio (sweet spot seemed to be about a 55-60% ratio, gpu to mem clock).