Stay with the 50 horse. It should weigh enough to make the stern squat down enough to keep the prop in the water. On the days with no wind you can go water skiing. I think that the extra weight of the 50 should only cost you 1 to 2 knots of sailing speed.
On second thought, stay with advice given in the other posts above.
What are you talking about?! That didn't stop the latest MacGregor 26, with that 60hp THING.
Is it me, or does anyone else think that thing looks a lot more like a powerboat with a sail, than a sailboat with a motor?
I'm sorry...that thing is a joke that floats...