AMD have just recently released a newer card (HD 7xxx series or higher) in the class of the HD 6570, the HD 7730 (class being GPUs that have a tdp of 50Watt or lower)
Brucifer couldn't yet have bought one of those when he wrote that, and it remains to be seen whether a HD 7730 can outperform a HD 6570 on BOINC.