Originally Posted by EdIsMe

I think the case for 650 is just an example of cons outweighing the pros.

Upsides: Maintaining geometry through size ranges, no toe overlap, shorter draft profile*note below

Downsides: Increased tire/tube expense, tires wear faster due to smaller size, bearings wear faster, brake tracks wear faster, a much larger gear ratio is needed to maintain the same speeds, rotational inertia is significantly decreased reducing high-speed stability with virtually no real benefit to handling, and probably more I can't think of at the moment.

*to the note above, smaller wheels were originally intended to be used for team time trials where bringing the 2nd rider closer to the rear wheel of the first, the draft effect would be increased. There was virtually no difference in aerodynamics from a solo perspective. I think given the highly specialized niche of the application lead to the eventual downfall. It was a solution without a problem and eventually everyone defected back to the standard 700c/27in.

On the geometry discussion, I am also the opposite of Aki. I'm only 5'5" but have an inseam of 30". My proportion difference isn't as great as his, but with today's super compact geometry being so prevalent, it's a problem.

Also, @rpenmanparker, you have it backwards. A higher number for seat angle means a steeper seat tube, bringing the saddle closer to the head tube, theoretically. In reality, the distance between the seat tube and head tube remains relatively constant as the effective top tube measurement, which results in the correlation you mentioned. If you consider the ratio between effective top tube and seat tube, you'll find that proportionally, smaller frames are designed much longer than their larger counterparts. (Larger torso, shorter legs). This is largely due to the industry's "try to fit as many people as best as possible" policy. Most shorter people also have shorter legs, particularly women, hence women's geometry.

To elaborate, a 47-50cm seat tube fits me just fine (on a 74* tube with ~20mm of setback and saddle clamped about center). Typically this will put top tube length for me in the 51.5-54cm range. With a 51.5 top tube, a 110mm stem, very compact (3T Ergonova) bars, and about 15mm of spacers under the stem (on a 100mm head tube) result in a very stretched out position. Any longer than this and I simply can't reach. On the Kilo I have a 47cm seat tube, approx 8" of seat post, saddle in middle, 51.3cm top tube, 100mm stem, 15mm of spacers, and classic ITM Anotomic bars (unsure of exact model) which have 95mm of reach c-c.