Darn you. I'm Bi-Cycle-ual and proud of it!Bunch of weirdos..
Oilhed, I have a 80/100-21 on the front & a 100/100-18 on the rear of my old XR250L. Maybe more extreme than the 18 or 19 than you were looking to compare. The difference in performance off-road is quiet dramatic. The XR is much more of a performer in the dirt and sand but I can't say it is just because of the tires. That's a personal choice. I mean it was designed just for off-road with all the accessories to let you ride on the street too.
The TW will happily plod along and do whatever you ask of it loyally. Not great at any one thing unless to dial it in for one specific task. It's an every-thing bike.
Both are comfortable at 50-55-60 and more if I want to push it. The TW has a 47T sprocket and the XR has a 44T (stock back in 1991 was 40T).
If you need to go faster you'll probably want to look at a bigger bike. Gearing fast for the pavement will make them suck-ass with less torque and bottom-end on the trails.
The second small dual-sport bike I ever rode after the TW was a 2006 XT225 that a friend bought. I really liked riding it and it's so frickin light and 6 speeds is the way to go.
Another buddy has a 2018 XT250 and is very happy with it. It is fast out-of-the-box but I have not personally ridden it yet. He did ride my TW but wanted just a bit more "umph".
Apples and Oranges no matter what you compare old or new to a TW. You can get away with faster speeds and control with the bigger and thinner tires IMO.
But the TW is Big-Boned and the happiest bike I own.