My butt tells me that the Pro (as well as the Ideal 90) are a bit like sitting on a banister, they divide and conquer (or is it "lift and separate"). The B66 is nice for short runs but after a dozen miles the springy action starts to chafe. The B-17 feels really nice and supportive.
I don't put lots of miles on my bikes, though and most of them have their Northroads bars turned up, tourist style.