The problem is that the manufacturer wont admit that your card is faulty, I wonder what would you tell them to describe your problems? I'm pretty sure you wont tell them you are doing mining.
back to GPU prob, Ensure that you have a pretty decent PSU to handle those monstrous power hunger cards.
Yes, that is always the dilemma. 1600W supply with a 750W so power isn't the problem.... I have made some progress. These cards will do well over 800 h/s on equihash at 100% power... but there seems to be a relationship between core and mem. E.g. by default they overclock it appears so even a 0+ on core will run them at a 2000mhz core clock, they are garanteed for 2025 core. and can run up to 2100mhz. So I've backed the core clock back to +0 and the mem clock back to +550 (from the +850 I was running). Seems to have made a difference. I noticed however when I pushed the mem clock back down, the core clock decreased as well. Curious. haven't changed the power and maybe that is why it's limiting internally.
Anyway, it will run DSTM just fine on any of the numbers above.... but this one card, when you stop DSTM, will go into in a race condition with it's IRQ's. So the battle continues, but I have made some progress