X
-I 18 --gpu-engine 1150 --gpu-memclock 1500 -g 2 -w 256 --lookup-gap 2 --thread-concurrency 8192
That gives me 3.345 Mh/s running in closed case at 70 to 72F
I think I read somewhere that if you put i=18 to 280x you will fry them.
( same as if you put more then i=20 to 290 cards )
everybody can correct me if I'm wrong.

280x and 7970ghz running for over 11 hrs
"intensity" : "20,20",
"xintensity" : "0,0",
"rawintensity" : "0,0",
"worksize" : "256,256",
"kernel" : "x11mod,x11mod",
"lookup-gap" : "2,2",
"thread-concurrency" : "8192,8192",
"shaders" : "0,0",
"gpu-threads" : "2,2",
"gpu-engine" : "1150-1150,1150-1150",
"gpu-fan" : "100-100,100-100",
"gpu-memclock" : "1650,1650",
"gpu-memdiff" : "0,0",
"gpu-powertune" : "20,20",