So I took my 1984 300SD out to the only area of our freeway to allow 70mph legally then broke the law and got it up to 100mph for about a mile or so. Blew quite a bit of smoke accelerating from 80mph to 100mph. I repeated this pattern three or four times. For the first time in months I finally brought the temp up to 80C. It seemed to work wonders. While still at 80C, and at reduced speeds, shifting from 1st to 2nd was much smoother. Acceleration was improved as well. Obviously, no smoke afterward either, even at reduced speeds. Question is, how long does this benefit tend to last and is there another way to accomplish the same thing without excessively speeding? Do I need to find a race track or move to Deutschland?

The best way is to find a long hill/mountain.

If it took 100mph to reach 80*C then it means you have a bad thermostat and/or temperature sender.