I've got two bikes equipped with B.17 saddles. I've had the orange one for 30 years, and the green one for 20 years. Both are somewhere around the 50,000 mile mark.
Both have pretty similar geometry, and both saddles are pretty close to level (as far as I can tell).
I have to admit that I'm intrigued by those who need to tilt the saddle up or down significantly. My first reaction to nose up saddles and the argument that it is needed to avoid sliding forward is that the saddle probably isn't far enough back. The limited degree to which Brooks can slide back might be a factor, plus the increase in seatposts that don't offer much rearward offset.
As far as nose down saddles... I have no familiarity with that or why it would be preferred.
Steve in Peoria
(my Brooks Pro's are fairly level too)