Here is an interesting comparison over 100 shoes.
The first picture shows where all the BB pairs are on the left and all the PP pairs on the right.
[attachimg=1]
The second picture shows where all the BP pairs are on the left and all the PB pairs on the right.
[attachimg=2]
Notice the much longer gaps in appearance throughout the shoes of the BB and PP as opposed to the BP and PB. Of course there are more 1s than 2s etc... But it's interesting looking at it in a visual context just to see what actually happens.
It's a possible angle of attack.
cheers