Max MPH with single DC driveshaft???

Doing research on a one-piece double cardan driveshaft for my '13 4x4 DCSB. I've called 5 or 6 custom driveline shops around the country. Two of them (repped by folks on TW) said a one-piece was a very bad idea because of "jump roping" when nearing critical speed. A local shop wanted to make the driveshaft 4" in diameter for added safety margin (4" won't fit without cutting the carrier bearing mount). Most places I talked to said the max speed with a 3.5" steel one-piece driveshaft that's 67.375" long is around 80mph.

My question is, for all of you that purchased one-piece driveshafts, did the shop give you a max MPH speed that you should never exceed due to safety issues?

 

bump..

 

I don't think you can have a dbl cardan/1 piece driveshaft.
As far as mph goes a lot of variables

 

I know the thread is old, but if you google driveshaft rpm calculator, some of the driveshaft component mfgrs have online tools that will calculate the max rpms of a given driveshaft. Then you have to do the math on how fast you can go at that rpm. I.e, I have tires that are 33.25 diameter (roughly), 4.56 gears, and my driveshaft is spinning appx 3000 rpm at 80 mph. My single piece driveshaft is 4" in diameter. I can't remember the terminal speed, but the shop said they balanced it at 3500 rpm.