I have no idea. After all, the important dimensions for setting up your handlebars on both bikes is the "stack and reach" (i.e. the vertical and horizontal distances from the BB).

Also, toptube length is pretty well meaningless for frame sizing if you ask me since it's highly dependent on the seat tube angle and head tube length of the particular bikes. It's not a very good dimension to compare things with IMHO.

Figure out your Tri or TT bar position with an adjustable stem (such as a Look Ergostem) and then choose a TT frame that has a good stack and reach for the particular bar configuration you've chosen and results in the use of a reasonable length stem.