Ideas on power choice
Aren't Cubs supposed to fly like trainers ?
While I've used Motocalc for years I've never really used the Moto-opinion bit, I just look at the numbers myself. And I always switch the motor heating feature off because it seems to me to give more accurate results. Personally I'd put a geared 6V S40 and 7 or 8 cells in it, prop it for about 10-12A and fly it. I wouldn't take too much notice of static thrust figures, the plane will spend almost all of it's life far from static. If MCalc shows a reasonable stall speed and a reasonable flying speed range it should be o.k.
Putting bigger heavier motors and batteries in a small plane rarely works well. If you really want a lot more performance then small brushless motors are the only way to go, but they're not cheap. All you will gain from Li-poly batteries is slightly lower weight. They're good for extra duration but not really for extra performance.
Steve