how are you getting 750-760 on your 280x? What brand are they?
I can only get 700-710 on my 280x's
they are asus directCUII non TOP versions. (earlier ones with a 2 space cooler not three)
I use the cgminer.conf file not a batch.
amongst other things the main criteria are -
intensity 13
powertune -20
clock 1130
memory 1780
been running for a couple of weeks now, no HW errors as long as I don't clock any higher.
Had them running 780kh/s for a few days but not so stable.
hope that helps buddy
Ive got the gigabyte OC 280x's with the 3 fans..
The best i could get was with 1028engine, powertune 0, and memory at 1500.. I havent actually tried adjusting the memory.
In saying that, i've since power modded them from 1.2 volts to 1.091 volts, and its reduced power consumption by approx 60-80watts per GPU.
Whats the voltage set on those asus cards? that might be the key to the speeds your getting (copy/paste of cgminer after pressing G?)
Thanks.