Smack me in the head. I forgot to update the drivers. I have an activediskimage already set up to go that I just load onto new rigs so everything sets up in a snap. The 7970s run like champs on the older drivers, but the 280x's are now running better with the new drivers.
Catalyst 13.12 and SDK 2.9
After trying a bunch of the typical random combinations and scenarios I've settled on these settings for now which get 729s'/749's +/- respectively. So much better.
--lookup-gap 2 --thread-concurrency 11200 --shaders 2048 -g 2 -I 13 --worksize 256 --expiry 1 --scan-time 1 --queue 0 --no-submit-stale --gpu-vddc 1.131 --gpu-engine 1020,1050,1050,1050,1050 --gpu-memclock 1500 --gpu-fan 90 --gpu-powertune 0
I'll have to spend some time seeing if I can get vddc any lower "round the clock stable".
GPUZ reports 1.039-1.078 using 1.131 in cgminer, so I guess that seems pretty good.
Oh yeah, and you guys rule
Now that leaves the throttling issue on the cards that get over 73C which I know everyone seems to be having, I think I'll make a special thread for that.