My experience with B17s is that if the drop is too great I will slide forward on even a dead-level saddle. It also causes my hip to pop in and out viciously (other things do this too, not necessarily a cycling thing) and is just generally uncomfortable. I've heard it said many times that you shouldn't use a B17 on a bike with much drop and I find this to be true in my case. I believe both the sliding and the general discomfort is because of its width, in an upright position it's fine. I haven't had the necessary funds to try a narrower model.