CV Joint is the weak point
The U-joint on the stock front driveshaft is stronger than the 1310 but not as strong (as I understand) as the 1350 (I've heard it described as something around a 1330). The main problem, however, with the stock driveshaft (besides the obvious likely interference with the exhaust with a normal lift) is that (even if the boot is intact) under a heavy load, the CV (Rezeppa) can just open up like a can of tuna and the balls are displaced from where they should be and the CV joint fails. An advantage to aftermarket double cardan driveshafts (1310 or 1350) is that all of the articulation is with U-joints. An advantage with the 1310 is that, with the smaller U-joints, they can move over a greater angle than the 1350 allowing more articulation of the suspension before the joints bind. Another is, that with the smaller diameter, the suspension can move more before the shaft hits the exhaust. A 1310 shaft should be strong enough for most rock crawling with tires up to 37". If you go bigger or are hyper-aggressive, you'd be better off with a 1350 though that would likely suggest an exhaust system mod as well.
