the earliest Trek 800 had mainframe cromo tubes
later on trek cheaped out and did SEAT TUBE cromo-the decal will tell the story.
and later still went to aluminum
The mainframe cromo would be most desirable
but frankly I can tell any RIDE DIFFERENCE between ANY of them-certainly not the seat tube vs all 3 tubes
Yeah they are nice bikes.Ride well-sturdy-great "better than beater" bikes.