Best tip I can offer to anyone struggling with good settings is to try backing off on the engine clock. After setting up my R9 290 card to mine LTC, I switched to VTC and spent about a week struggling with instability and driver crashes (I could either mine at 200kH/s, or 300 for a few hours at most). With version 0.5.3 of vertminer, the fix for crash on quit made it a bit easier to tweak the settings, and I have had 400kH/s steady for a couple of days (less a couple of short breaks for gaming).
I was mining LTC at clocks of 1049/1450, and not great hash rate, but it seemed OK.
Settings:
"thread-concurrency" : "25600",
"gpu-engine" : "896",
"gpu-memclock" : "1498",
"intensity" : "18",
Temps 80* at 85% fan (20* ambient)
There seems to be something odd around I=13 for me, below I get 10s kH/s, the same as after the driver crashes. Also only a cold start seems reliable at getting the effect of new settings al the time.
The process was: Set I=16. Make some guesses for TC, find something that looks good. Adjust engine clock up/down in steps of 30MHz to find the best. Experiment with reducing mem clock, and small changes in value (ideally with also changes in engine clock to look for a peak). Finally push up I to the point when it stops improving (so being backed off a little from the point of generating too much heat, and being too sensitive to hardware errors).
A:605862 R:1142 HW:0
Edit: Just remembered after seeing a post on the main thread, I had a crash early on with VTC where the clocks seemed to get stuck too high (even after a cold boot which was the only way I could even get a stable desktop). Need to go in with a GPU tuner to set them back to near stock (mem clock ended up at 150 MHz once too)
Before my tweaking I was getting HW errors but overall I seemed to win from increasing intensity. All gone now though.