I have 3x Sapphire Vapor-X R9 280x running at 1080/1500 undervolted with SAPPHIRE TRIXX to 1137

intensity 13, thread-concurrency 8192, GPU-THREADS 2, shaders 2048, -w 256 --auto-fan 0-95

750khs each


Asrock motherboard and amd cpu. I was having problems until I disabled the onboard GPU in UEFI/BIOS. You might want to check that out. (you could check without disabling in bios by starting cgminer with -d 0,1 (gpu 0 and 1, if those are your R9's)

And define heat problems? they are supposed to run like 75 degrees. I use 2 boards to run 3 cards (I use two cases too, duh. Cooler master Haf X and a Storm Trooper)

My fans are at 1500/2500rpm and temps stay at 72-75degress , I use autofan

PS

the other card is run off an asus intel motherboard with an i5 CPU , same settings and same hashrate @ 750khs

Oh and running Windows 7 ultimate with latest amd drivers 13.9 and latest gpu capable cgminer 3.7.2