I've followed this thread with some interest. It is an ongoing amazement to me that I keep learning more and more about sizing and fit even after so many years riding a road bike.
I've found that older bikes with slack angles, lower bb shells and longer stays and top-tubes tend to be very nice in slightly larger sizes. If my racing size is 55cm c-t, a 57-58 cm c-t in a frame of this older style will not only be more comfortable for me in general, especially on longer rides, but overall handling seems...easier. I notice that my position on these larger frames always seems ideal with regard to weight distribution and body position, although I suppose you could achieve the same thing on a smaller frame. I've tried, though, and it's not quite the same, even on a smaller frame with the older geometry.
I recently bought a 58cm c-t Bianchi Competition from the early 1960s, with just a little seatpost showing when it's set up correctly for my leg-length. It rides like a perfect ocean-liner, with plenty of refinement, and I don't especially notice that frame is a bit big. Sure, a 57 or 56 would probably feel better in some ways, but a bigger frame of this kind is perfectly fine too.
Problems crop up for me with later-style frames, with steeper angles, higher bb-shells and shorter stays and top-tubes..I really notice it when those frames are even slightly outside my ideal size of 55-56cm c-t seat and 55-56cm c-c top. I've bought and sold a lot of really nice criterium bikes of this sort..they never seem to feel right. They just feel too big..as if the bike's riding me instead of the other way around. Maybe there's something less forgiving in general about these later, more aggressive frames. They're certainly rideable..the effect can be subtle. But I'm at the point where I don't have any even slightly oversized bikes in this later style.
It's because I'm getting older..but I find those later aggressive criterium bikes to be distinctly unappealing. Such bikes seem to have been designed for a lot of seat-post showing, and long stems. Ride one in a size larger than ideal and they just don't feel right. The earlier road geometries, with the long stays, low bb and slack angles, esp slack seat-tubes, feel better and better as the years go on and are more forgiving of variations in fit.
Charles Andrews Los Angeles
It is impossible to begin to learn that
which one thinks one already knows.
--Epictetus