Yeah, I can confirm that for sure. My ATI card isn't bad by any means, but I have to run this game at almost the minimal graphic settings to even stay above 30 fps. I just hope this game gets optimized for these cards more in the future as I don't plan on upgrading my GPU anytime soon.
Since this is a UDK game it uses PhysX and NVIDIA hard-coded PhysX physics to only run on the cpu if an NVIDIA card is not the primary gpu. That's why this game runs so bad on ATI gpus.
The only way for RenX to run decently on ATI is if the devs remake the game on a new engine.
Obviously I don't expect that to happen, so don't get your hopes up.
Ah well. That's good to know, though. As long as the occassional temporary lock-ups that happen when something explodes isn't caused by this card, I'll deal with it for now.