Thanks so much for the helpful advice! I've been reading lots of geometry charts, and it finally just clicked for me how the seat and head tube angles, top tube length, and stack height all work together to affect reach. Eureka! No wonder a 51 cm top tube can seem long to me- I have to scoot my seat way back to get the proper setback for my femurs, which effectively lengthens my reach. And on a small frame, the drop to the bars puts me in an aggressive position on what, for other people, would be a more upright bike. Darn these short arms!

I've got a chart going that plots reach and head tube height for each of the bikes I mentioned in my original post. In my size range, the Giant Avail Advanced came in with the shortest reach/highest head tube combo, with the Ruby and Synapse in a tie for second place. I'll research each of the brands mentioned above now and add them to the chart. This stuff is so interesting!

I've also spoken with several fitters, and I've narrowed the field down to a couple who seem particularly promising.

Thanks so much for the suggestions!

Gillian