The Trek 600/620/630/640 siblings rode the same frame geometry and tubing, but differed in color and obviously spec, which also, to whatever degree, defined their purpose. For any frameset hunter (like me), it's basically a case of pick your color and go.

The 700 model was a TX700 in its previous life (in name mainly) as a slightly longer (in the chain stays) all-around bicycle. It returned in 1986 for one year as a very nice sport tourer (425mm chain stays).

I had a 1983 one-year-only (as a road bike) 970. Very nice bike/frameset. The 970 went MTB/ATB/hybrid in later years, and was a 950 (frameset) before 1983, and a 930 before 1981.