"There isn’t any means of controlling the VDDC (VGPU) voltage on this card. There are some utilities that seem to work like TriXX, but it will not in any way set the voltage. You’re stuck at 1,188V and you’ll have to make the best out of that. With that said, we managed a healthy 1125MHz in the core and an impressive 1,550MHz on the Hynix GDDR5 memory. Some benchmarks we could complete at 1,150MHz but that was not stable to run through the entire suit we used. Thus we settled on the lower frequency. We suspect that for everyday use one will likely want to employ 1,100MHz or perhaps 1,075MHz for that added safety. Of course each model will vary and our particular card according to GPU-Z had an ASIC quality of 67.9%. Not great by any means, yet we managed a healthy 170MHz overclock for our tests. That is impressive by our measure, especially given that we had nothing but the TDP power limit slider and fan speed to work with.
Talking about the fan speed again, at full throttle it managed to keep the card form going above 65’C even with the overclock on both the core and memory. This was in contrast to the normal fan profile which capped temperatures at 71’C. It’s very obvious that this is one capable cooler that PowerColor has built."
http://www.theoverclocker.com/powercolor/
For someone like you with a 570, I'd look towards a faster card as I don't feel R9 270 is a good enough upgrade. I think you should wait for an R9 280X/290 to drop to $170-180.