There are certainly some here much more qualified to answer, but here's what I've learned:
The frame sets shared the same geo with the difference being the tubing. 5XX = Ishiwata, 7XX = Reynolds, 9XX = Columbus. I believe the tubing thicknesses were incredibly close, if not the same. I'd argue the greatest difference between these frames is the aesthetics of the tubing decals. This all pertains to the early TX series frames. The first number represented the tubing, the second number the style/geo of the bike, and the third signified the bike's groupset. This becomes clear as you look through the 77-81 Trek catalogs. Once you get to 82, they still adhered to that general system, but it became more nuanced as more models were added.
My comment about the 910 is solely based on the fact that I've seen far fewer 910s than 710s or 510s.
Last edited by Rooney; 10-12-23 at 11:50 AM.