Shimano BB for Hollow Tec
 

Is there a quality difference in the bearings in the Shimano selection of external BB's?
Thanks!

Depends on what quality you are looking for. While the Dura-Ace will have the best performance quality, the Ultegra and lesser might last a tad bit longer. Very much marginal gains with all of it. You can't mix all of them willy nilly. So make sure to look at what BBs go with what shell size and crank. The hollowtech mtb cranks and road cranks aren't all the same spindle length.

I have ultegra, 105, and 4700 level BBs. I cannot tell a difference in how they spin. I've not had to replace any of them. I would guess the 105 has the most miles, but all are well used.