LDM, I am NOT the most experienced contributer here, but my own experience is that this model has a lot of drag and a lot of weight. I would personally be very leary of trying to power it with a .91. I have an ASP 1.20, and I wouldn't want anything less. My plane weighs in at about 12lbs, which seems to be typical of most. Mine is put together pretty much as recommended by the factory. I do, however, have the additional weight of the CJ pneumatic retracts and a lightweight, robart retractable tailwheel. These additions also require a couple extra servos. I need to experiment more with props. Currently have a 16 x 6 and I'm no where near unlimited verticle. If I point it up, I better have a plan in mind for coming back down! For instance, big loops are marginal and must be entered into at top speed. This Hellcat seems to have plenty wing though. Mine flys stable at low speeds. Takeoff roll isn't especially long. Reduce power and she really slows down fast, so landing approach is made with a lot of power. In my opinion, go with a 1.20 if you can.