AoC runs a lot better than my 8800-320 did also. The IQ is a TON better, which may be due to a larger framebuffer too. I run everything on high, 4x AA, shadow resolution low, bloom off, cache maxed (it's 200 something mb), and the grass draw distance at around 100 and get mostly 40+ in Tortage. I'm just not too pleased with AoCs progress and haven't put much time into it lately.
The results aren't quite as dramatic as TF2, but ATI is also working on better drivers for it. The word is that Catalyst 8.7 will have AoC specific fixes in it.
edit: HardOCP did a review for the 4800s and included AoC benches.