Having owned and blown up a 6.5 maybe my input will be a little less obnoxious than everyone elses. First things first, go hit up a forum like dieselplace that has a good 6.5 following. They are not bad motors, they are probably just better suited for a half ton and its really tough to compare a 6.5 to the 12valves and evem 7.3 idi's which were both used in medium duty applications.
I had a 93 for a long time and i still to this day miss that truck alot. It would get hot towing other pickups and small tractors, but it was a fantastic daily driver. I sold the truck to my brother in law( well now he is my brother in law, at that point we were just buddies and i hadn't even started banging his sister yet LOL) who turned the fuel screw into the stop, advanced the timing as far as it would go, wired the waste gate shut and proceeded to abuse the thing for a year until i bought it back and put some gauges in it. Another year and a half of me pummeling it and it broke a connecting rod. I dumped in a short block out of a 98, made an adjustable waste gate actuator, dialed it in for about 14lbs max, turned the fuel screw down to about 1/2 turn over stock and she always ran well and got around 18-20 mpgs.
IMHO, a mechanical pump 6.5 is a great diesel pickup for a young kid, simple to work on, making it excellent for an entry level diesel mechanic that wants to tinker and turn it up a little bit. It'll be economical for all the running around and miles young kids tend to rack up, it will adequately haul medium sized loads. If junior pukes a motor because he tinkered a little to hard used 6.5s can be found pretty cheap.
Now if you want to talk whats faster, my 6.5 would absolutely annihilate a stock 24v. For you guys who dont remember what driving a stone stock un modded 2nd gen and older cummins is like, while they are hard pullers, they are noticeably slower than a 4 cylinder s-10 pickup.
