The C17 is narrower than the B17.

C17 Width = 162mm according to:
BROOKS ENGLAND LTD. | TOURING & TREKKING | CAMBIUM C17

B17 width = 175mm
BROOKS ENGLAND LTD. | TOURING+&+TREKKING | B17+STANDARD

I think the C17 is much closer to a Brooks Pro, which = 160mm
BROOKS ENGLAND LTD. | ROAD+&+MTB | TEAM+PRO+CLASSIC

A friend of mine did not like his C17, he loaned it to me, I suspect he was hoping I would buy it from him. I planned to give it a 20 mile test ride, but after I got a quarter mile, I turned around back home to put my broken in leather saddle back on the bike.

Some people need a long break in time on Brooks saddles and I am one of those. Other people like them straight out of the box. I think that the crowd that likes them out of the box is more likely to prefer the C17. But if you needed to break in your leather saddles, I suspect that the C17 won't be your first choice.

I was hoping I would like the C17 so that I do not have to worry as much about getting my leather saddle wet on a long tour where it would be hard to dry it out. But, it did not work out for me. I use a Brooks Conquest which is very similar in shape to the Brooks Pro. (On one bike I have a Pro.) So, the size and shape of the C17 was what I wanted. But that was not enough to make me like it.