The Gunnar geometry tables for the Roadie, Crosshairs, etc., say "Seatmast is measured from the center of the bottom bracket to the top of the seat tube." Thus, is their size "56" measured 56cm to the top of the seat collar? Or to the top of the top tube? Or somewhere just under the seat collar? :confused:

http://www.gunnarbikes.com/crosshairsspecs.php

The top of the seat tube is about 1/8" under the top of the seat collar.
Since the new Gunnar's are more "compact" than they used to be, the only dimention that is critical is the virtual top tube length.

The top of the seat tube is about 1/8" under the top of the seat collar.
Since the new Gunnar's are more "compact" than they used to be, the only dimention that is critical is the virtual top tube length.

I'm asking cause it will be my rain bike and I want to make sure I can clamp it into my repair stand by the seatpost. So a "56" is 56 cm + 1/8th inch to the top of the seat collar?

Yes.
The seat post clamp that they give you with the Gunnar, looks like a piece of cheap crap. I recomend that you get the Salsa "Lip Lock" to replace it.

My understanding is the 56 is the measurement to the virtual top tube intersection. Seat mast is the actual distance to the seat collar. On a bike called a 56, the seatmast measurement would be less than 56.