From comparing the speeds I'm getting to hdminer, the miner isn't 6+% faster, it's only 1.2-2% faster. I'm using Catalyst 11.4 without downgrading and underclocking the memory so the difference could be even less than that (11.5 is supposed to give it a few Mh boost and not underclocking it would increase hashing rates by 0.5-1.5Mh/s).
Have you used the modified phatk kernel yet. Some have been showing it to have a 2%-3% increase. I rather suspect that eliminates the differences between this client and phoenix. mrb even acknowledged that the recent change was one that hdminer already had. Which since, like you I suspect that the difference is closer to 2% rather than 6% makes hdminer obsolete.