For older cards, the OSS driver might end up being better than crapalyst.
Actually, it's the newer cards that are reported to have better performance with the latest OSS drivers.
This is a pretty recent development, though. A little over a year ago, everything I'd heard was in line with what you're saying. But when I heard about all the improvements in the recent OSS drivers, I took a chance and bought a box with ATI, just a couple of months ago, and I must say that it's been absolutely smooth, effortless, and 100% hassle free. With a 3.12 kernel (now upgraded to 3.14). And no catalyst.
If your experience is older than that, then I think your information may be out of date.
Not that I'm saying you should switch or anything. No skin off my nose. Just saying your data may be out of date.