Four Stroke .91 works GREAT! I fly mine with an OS .91 Surpass and it is so well behaved. 1/2 or less throttle for cruising speed. There is plenty of power for getting out of trouble.
I haven't used floats, but in the winter on skiis it is fine.
My latest build is a highly modified Senior Telemaster with Magnum 1.20 4-stroke. Bomb bay is the entire center section - I moved the radio components to give me an empty box. It holds 80 ping-pong balls! (Or about 5 lbs of tootsi rolls)

Back to your Question - YES go withthe .91 !!!