How low before a 2 piece driveshaft is advised

[MalibuKasey]

So.... Looking at all the LOWWWW trucks Ive noticed the one thing most (not all) have in common is the use of a 2 piece driveshaft. Assuming this corrects alot of binding/pinion angle problems. So at how low is it recommended to change? Im currently at 5.5/7 but getting ready to go to 6.5/8. Ive noticed most of Delmos trucks have the 2 piece as well.
So hopefully you guys can shed a little light on this for us. Any things to take in to consideration when switching to one or things to look for or even the right way to measure for one etc. Your knowledge is much appreciated.