David, here is how I answered the question for myself. I asked how much heavier is the 1.08 over the 91FX? Then I asked if the weight increase is worth the increased power.

I have the ARF with; OS 1.08/Pitts Muffler and dual elevator servos with FG push rods. Mine balaced with a 5 cell 1800mAh battery under the back side of the canopy. I am using an APC 15x8. This is my first real high performance machine and it will require some work on my part. I have four areas I am work on after flying it this summer are:

1) Covering scheme. It is not the best for visual orientation. Will recover this winter.
2) Weight. I want to investigate reducing weight with;lighter landing gear/wheel/axles. Eliminate FG push rods by moving elevator servos to rear and using smaller battery more forward. Small receiver, mini throttle servo.
3) Dead stick glide is about 1:1 (45 deg angle!!!!) Nothing I can do about this but point nose down and hope I make the field.
4) Try different props. This thing is pretty fast even at 1/4 throttle. May be a 16x6??

Marcus