After some reinstalling and testing I can confirm that the GPU acceleration actually works for me. It just doesn't register in any GPU load programs, probably because it's not actually rendering frames via GPU completely.
5g profile works reasonably well for me now. Around 60-70% CPU on difficult files. That's on a 2600K @ 4.3 GHz, 7950 Vapor-X radeon @ 1150MHz (1400MHz memory, voltages raised a lot to allow for it).