During testing I flexed the crap out of my front every way I could think of and I never saw any more spline, usually the slip would result in me seeing no spline at all.
If you wheel it, you will have trouble. When your front axle is under power and has decent traction, it will tend to walk forward (kinda like axle wrap) It will pull the diff. down and therefore pull the front driveshaft apart.
When I first build my first front drive shaft........ I had over 5 inches of out travel and it pulled apart on me 3 times on one weekend. Needless to say, I made another one with more "overlap".
