Depending on what kind of flying you plan to do, the OS 46FX does a really nice job on the SE. I have this engine in both of my SEs, and one is on floats. I haven't flown that one yet, but feel it will handle well. I won't be doing much "stunt flyin'" (Have you seen the movie Flech with Chevy Chase?) due to the floats.

I agree that the 91 will be awfully heavy for such a light plane.