Wow, the 6570 seems to be unexpectedly slow. The 5670 isn't tested but I guess I might be still happy with my choice back at the time to take the 5670 instead a 6xxx series since support was better in the free drivers at that time.
Though I thought the 6570 falls in the mainstream category and iirc. some of the devs said these would be easiest to handle. The small GPUs need lots of attention and care to work with a fair performance, the mainstream is nice but the high ends need again attention since the CPU and others might already be a bottleneck so you can't use their full portential.
But besides the little cards and the exception all of them show very playable framerates and that is a good thing.
Stop TCPA, stupid software patents and corrupt politicians!