Driveshaft length tolerances +/-?

I like to get my yoke in the tranny as far as possible without bottoming out. I've had some so long that I had to remove the caps to get the rear u-joint into the rear yoke, then slip the caps on and tighten it down; still no probs with bottoming. The farther back that front yoke is from the trans, the more prone to vibration they are.

Do that on a 4x4 that has a lot of rear suspension travel and you'll end up breakin stuff.