On the basis that we are only talking about HollowTech 2 External Bottom Brackets

Shimano HT BB2 Bottom Brackets are a standard design, and the fitting is interchangable with each other and other brands of HT2 BB's. The sizing is determined by the BB shell, this will be 68 or 73mm, the BB has spacers to compensate for this difference, and make sure that the fit is correct for the crank.

There is a difference between road and MTB BB's these are not interchangable.

You say you are getting 3-5k from a BB, that's good for a HT2 BB; dependant on conditions ridden in, if you want longer, would look at a Phil Woods, or when you BB70 fails, get the bearing pulled from it, and replaced with Enduro bearing. the shells normally don't wear out, just the bearings