I'm pretty sure the B60 and B6 have the same board, but the B6 may have slightly different parts and the board isn't fully populated. Missing the power amplifier section. The newer B60 has a toroidal transformer from what I've seen.
I have a B135, and Armaegis is right you get bragging rights. On a serious matter I kind of just fell into the B135, I was originally planning the B6/BP26 and 4BBST2 route when I just happened to come across one, I'm very happy with it.
The biggest difference between the B135 and B60 for me (power aside) is that all the features of the B135 can be controlled remotely, and it also has a serial port to receive commands via RS232, which is handy. Whereas on the B60 only volume and I think mute can be remotely controlled and no RS232. I really like the look of the B60r but with no remote power on or input select via remote I think I could only put up with it in a bookshelf style system in my study. Where the B135 acts as my hifi and home theatre centre.