degray,

I flew an OS 120 Surpass III w/ pump in my Quest last year, flying the Sportsman sequence in Pattern. I had no power porblems at all, just had to move the battery back, behind the wing, to obtain a neutral CG, by neutral I mean, when I roll to inverted I need very little down elevator input to retain level flight.
All other installations were in the stock locations.

All in all a good combo, don't forget to strengthen the landing gear plate, as with all ARF's, absolutely no knock on this plane, I do it with every plane I buy.