The mid-90's Multi-tracks max out just a bit over 40mm on the tires. Plus, they have really short top-tubes, compared to MTB's. My 53.5cm 730 has a 57cm effective top tube. Other than those two limitations (in my mind), those old Treks are great bikes.

My Karate Monkey has the same geometry as my 730, with the exception of the top-tube, which is 3cm longer on the KM. I love the ride of the KM, don't love the looks so much. My dream bike is my KM's geometry but with more traditional diamond frame looks. Rivendell's Hunqapillar and Appaloosa are close.