I'm not an expert on this, just sharing my experience. I have 2 different models of HIS 280x and one hashes at 730 and runs cooler, the other is at 620-ish and lower and runs hotter. Funny thing is the slower card is a higher end model I believe (1000 core clock vs 850)...  I tried them both on 2 different Windows 7 boxes, one with an old MB, one with newer. I ordered 2 more of the faster ones.... Weird because the cards are damn near identical.

The faster one - fan runs at 56%:
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1p
C:\...\cgminer.exe --scrypt  -o stratum+tcp:*** -I 13 --thread-concurrency 11200 -g 2 -w 256 -I 13 --gpu-engine 1050 --gpu-memclock 1500 --gpu-powertune -20 --expiry 1 --scan-time 1 --queue 0 --no-submit-stale

the slower one - if I run it at the same settings as the other card the fan goes to 100% and it gets overheated anyway (although it does clear the 720 when it's not throttled down for overheating), under the following settings the fan is 61% :
setx GPU_MAX_ALLOC_PERCENT 90
setx GPU_USE_SYNC_OBJECTS 1p
blah blah... -I 13 --thread-concurrency 8192 -g 2 -w 256 -I 13 --gpu-engine 1000 --gpu-memclock 1500 --gpu-powertune -20 --expiry 1 --scan-time 1 --queue 0 --no-submit-stale