Trek 800 ? Pretty lowend bike to throw money at. I wouldn't swap cranks or BB until they actually broke. I'd just stick with square taper UN 26, 54 or 73

Acera or Deore cranks from Niagara cycle.

But only when necessary.

With a little patience you could get a nice Trek 930 complete off CL for the cost of BB+cranks. That's a better bang for buck upgrade than what you're considering.

If you go to vintage-trek.com you could probablt nail down the year of your bike