I don't know if this is related to the wear and traction discrepancies that some have posted for the AVON 45/46 tires, but it might be.
The non B and the "recommended" B versions for the XX are significantly different tires. In a phone call last week, the US AVON expert described changes to the sidewalls and tread to meet the German TUV standards for bikes capable of 180+mph.
He said that the feedback on applications on XXs, Busa's, etc. has been "much more positive" with the non B versions . He also stated that the Z rated non Bs have been tested for long periods at these high speeds, but if you ran them in the 180s plus for extended periods of time in Death Valley heat, they "might fail before the B versions". Due to the compromises required by the Bs, the standard tire has proved to provide better comfort, grip and tire life. He said that if it were his Blackbird, he would use the standard tire and that as the word gets out, you will see fewer and fewer places carrying the Bs.
I expect that for liability reasons, this will not be AVONs official position, but he convinced me. I basically do "Fast Sport Touring", have never exceeded 180mph unless in an airplane, so others may think differently.
If you find pieces of me in Death Valley due to a tire explosion, then I may have made the wrong call.