I'm running 2x 5870s but at 965 core, 300 mem.

phoenix -u http://blah/ -k poclbm VECTORS AGGRESSION=11 BFI_INT PLATFORM=0 DEVICE=0 WORKSIZE=768
Gets me 404 MH/s

phoenix -u http://blah/ VECTORS AGGRESSION=12 BFI_INT PLATFORM=0 DEVICE=0 WORKSIZE=768 -k phatk
Gets me 420 MH/s

Huge improvement. Thanks for this.