PhysSurface will give you wrong results if you will not use Branched Path.
Illustration:
Setup
Branched Path
Path
Highlights from spots are too weak.
No such problems with pure Cycles, PoserSurface not tested.
Full story here: CPU/GPU render different outcomes
Illustration:
Setup

Branched Path
Path
Highlights from spots are too weak.
No such problems with pure Cycles, PoserSurface not tested.
Full story here: CPU/GPU render different outcomes