RE: Katana 50 by Hangar 9
What servos are you planning on using in the tail? If bigger/heavier than minis (i.e. Hitec 225mg size), you'll probably want the heavier motor to help balance. If it were me, I'd go with the lightest setup possible, as the plane already is on the heavier side for a 60" plane...
Also, forgive me, as I don't remember what your planned usage is for the plane, but what kind of flying do you intend to do? If it's 3D, definitely go for the lightest motor/battery/servo setup. If it's general sport flying (sounds like it, with your intended 8min, 70% power flight times), I think it'll do fine with whichever setup you decide...