Like DragRacerSBC mentioned, shaft critical speed is really important. The chart from MW is a good reference and this handy calculator from Spicer is another. Somewhere between is the two critical speeds for your driveshaft tube length. Spicer uses 50% critical speed as a conservative recommendation, MW is closer to 100%, and my vibrations book uses 75% critical speed as max speed operating point.

A call to one of the mentioned driveshaft places should get you on the right track as this is a perfect example where saving a dollar could hamstring you if you decide to step up your performance level later.

https://spicerparts.com/calcul...ating-rpm-calculator