It would be nice to get a more "official" confirmation but my dealer technical person told me that they told them at the dealer training that "B" engages "something else in the system" and it is not recommended to drive with it all the time. According to him "B" is not just recuperation step 4 but "something else".
I too prefer the "feel" of "B" and would love to hear some official statement that recommends for or against it.
FWIW, for the 4 weeks of freeway driving in LA i have done (included 2 hills), i can't say i see a whole lot of range difference between plain "D" all the way to "B". It all seems to even out at around 4.2mls/kwh in the end, which is a number i'm quite happy with.