I've looked at a number of 650B converted 25.5" (65cm) Treks and they don't look good/proportional to me. Smaller sizes? All day. 700C and big tires on an already tall and long wheelbase tourer looks proportional. Big bike compositional issues to work through, but we get there. If it's comfortable now, it only gets better with supple and much lighter tires! 650s would look bad on my 620 (which is now into the 'shop' to get its canti posts replaced and positioned so that it can work with TRP mini-Vs for a big brake upgrade). 700x42s all day.