So, after some benchmarking with unigine heaven, I have settled on core speed of 1155MHz, and memory set at 1499MHz. I also set the power limit to the max. Voltage is still not adjustable. It was able to run a little higher, frames hung up a few times, and I think slight instability was actually causing it to score less.
With the somewhat arbitrary settings(though the same for each test), I was able to increase my FPS from 58.2 at out of the box settings, up to 67.8, give or take a few tenths of a frame. And this card starts out a little faster than the standard 270 to begin with.
I'm playing Battlefield 4, 1680x1050(max on my monitor) Ultra setting, and getting an average of 55-65 fps depending on the map. When I bought it I was hoping to play at high settings, so I'm pretty happy.
Pretty fricking good for $179us, and it came with a $60 game that I was going to buy anyway.
A few notes, All of the tests were run with the fan at 100% and the side cover off my computer, because I have the worlds cheapest(and sharpest) case with no fans. Also its near a drafty door, so ambient temp was probably in the 60's F. Core temp never got past 55C. Using higher clock speeds while playing BF4 caused crashes, 1155/1499, played stable for several rounds, but I have not given it a rigorous day of gaming yet.
As you mentioned It is pretty unlikely to do damage by overclocking, usually weird stuff starts happening, and you just back off a bit, sometimes it will crash the system though, so make sure you backup anything on your HD that you cannot afford to loose.
Anyway, I am getting an extra 15% out of this card past the factory OC, and that is better than a reference 270X.
you could probably get a solid 60 FPS at lower resolutions, or by lowering just a few settings in games, keeping most at ultra.