I was a Brooks Imperial seat tester before they were released, mine is a pre-production model. I also have two bikes with a B-17, one with a B-68 and one with a titanium rail professional. In my opinion each model has a slightly different focus. The Ti-pro is on CAAD 9 with handlebars below seat, for riding fast and mostly looking at the road-
comfortable for me. The B-17s are on my commuter bikes, with handle bars above seat and a fairly upright seating position- comfortable. The Imperial is on a sport touring bike with handlebar and seat about level and relaxed seating position- very comfortable. B-68 is on a very upright winter commuter comfort bike- comfortable. Over time, I've swapped the Imperial among different bikes. The Imperial on my commuters and comfort bike - was good- perhaps not as comfortable as the well worn B-17s or B-68. The Imperial on a Trek 520 was very nice [primary test seat]. Imperial on the CAAD, nice - but the Ti-pro is very comfortable there and weights less. So the Imperial is probably optimal when the handlebars and seat are about level. Downside the the Imperial - none. One caveat - it did seem to take a lot of adjustment to seat angle and position with the Imperial to get it just right. On the right bike and adjusted this Imperial was and is the most comfortable bike seat I've ridden on [been biking since 1960].