I'm not on 12 but I use the Poser preview renderer quite a bit in 11... I disable hardware AO entirely as I find the results in preview not very good, I crank up my preview texture display to 4096 so I can preview my textures, as I modify and work on them in Mudbox and photoshop, accurately without so much more time costly rendering. I'd dump the scene preview AO as I think it's inferior to actual GI occlusion... tends to be splotchy and is just a frill for scene preview, could save you some processing power.