"Greg Milligan" wrote...
I'm interested in a plans-built amphib, and the Coot and Osprey II have
attracted my attention. Any thoughts/opinions about one vs the other?

On a related issue, I have been underwhelmed by the useful loads of both
aircraft...around 450 pounds, more or less. Is there any "conventional
wisdom" out there about "supersizing" a plane; i.e. building to 120% or
so
of scale?

Vulmer-Jensen VJ-22 gives an adequate payload:
http://www.volmeraircraft.com
http://mars.ark.com/~dcf/volmer2.html

If you wanted to go the kit route visit he
http://www.glassgoose.com
Better payload and speed...