Striker,
I flew mine with a .91 all last summer with the tank on the CG. I started out with the tank in the nose and the difference in flight charateristics is noteworthy to say the least. With the tank in the nose you sart out several ounces nose heavy and get more tail heavy all through the flight and it's NOTICABLE. With the tank on the CG it flies the same from take off to landing and maneuvers like hovering and water falls are easier since tail heavy planes do them better.

I fly mine with the CG at 6" back and you have to "fly" the plane into a landing, it will not simply sink in once the throttle is chopped, takes getting used to but isn't a big deal. The .91 OS will do everything you would want to do with the plane, except on very hot days in the summer, will not pull out of a hover under those conditions.

I finally broke down and got a Saito 100 and the performance increase was well worth the cost. On hot days it pulls out well and on cool days it's a rocket, worth every penny I spent for it. I have been running an APC 15 x 6 and 15% Wildcat fuel with BOTH of my engines. I tried 15 x 4W and the 16 x 4W and didn't like them as much as the 15 x 6 which seems to offer a good combination of hovering power and level flight speed that isn't too fast for the plane..