As someone who has long been on a vision quest for a taller, decent-quality mixte, I'd say go for that Koga-Miyata. Beautiful frame there. You could compromise on the tire thing--I was a 25c diehard for a long time, but I went to 28c on most of my bikes and haven't looked back. Aesthetically they don't look that much bigger than a 25c, and they don't feel unweildy or noticeably heavier in any way. Get some good pads for those cantis--can't go wrong with Kool Stops--and you're good to go. Look forward to see what you end up with, at any rate.