I have the Gp Ultimate with a Saito 91 installed, flies great, unlimited vertical. I like the Gp version better because I can throw it in the my van, or the trunk of car, all assembled. Get to the field and pull it out and fly it, no messing around with the stuts,cabanes, and pushrods. If you wanna stick with a 2 stroke I would go with an Irvine 53, a 46 will fly it fine, but it is just ever so slightly underpowered with the 46. The Saito 91 is awesome in this plane, and the weight of the Saito 91 isnt bad at all, a couple of ounces heavier than a 46. Good luck, Daz...