Why not use 7950's for lite coin mining?
4 7950's would hash around 2000 kh/s 4 7970's will hash around 3000 kh/s.
Mind sharing what bios version and/or gpu clock and memory setting you used to get 750kh/s of these 7970 dual-x OC?
I only get 715kh/s on mine with 1015/1425 with cgminer and have it run stable without crashing for days.
Using default bios that comes with the card - version: 015.025.000.099.000000