I LOVE my 3208 Cat! It's a huge engine for a bus. She'll pull uphill and walk away from everyone else without even trying. Matched with a 643 transmission and new 4.11 rear gears, she'll do 70 m.p.h. all day long. My Thomas handles the speed and cross-winds without any issues.
Look for the older Thomas buses (1998s or older) that have that combination and you'll be very happy. If you keep the bus under 63 m.p.h. (with the above set-up) the fuel mileage will go north of 12 m.p.g. depending upon terrain.
Like any manufacturer, Cat made some turkeys in their time, but the 3208 is NOT one of them. One of the rare V8 diesels, there's a lot of engine and reliability packed into that set-up.
Best of fortunes in finding what you're after!