OOH am I jealous! Where did you get the kit/plans? I had my eye on one at a LHS, but they went out of business when I wasn't looking )-;

I am currently (no pun intended) flying a 16 foot MM Glder Tech (?) floater on an Aveox 1010 2Y with a 4.4 planetary gearbox, 12 cells 14.5x7 Cam folder. More than enough power. I have flown it with a stock Master airscrew 05 and 3.5/1 gearbox, seven cell, ( prop?). No screamer, but it got up there just fine. An Astro 15 cobalt with stock gearbox on 10 or 12 cells would do a great job. I don't know what your financial constraints are, but you could aslo check out the AXi motors at the Model Motors web site.

Hope this helps. would love to see a pic.
Walt