also am very happy with my B17 and a seat/bar drop of about 2-2 1/2 inches, fine all around.
I would go with the regular, not the narrow.
I would suggest doing some forum searches on stuff people have written of their Brooks experiences. I second the point on being careful and observant of seat positional changes and how they change how it will feel. As with any seat adjustments, do small ones and really pay attention to the feeling. One issue is that they do not have marks on the rails, so a piece of tape will help in seeing fore and aft adjustments better.
Also on breaking in period (mine, not much more than 6 or 7 one hour long rides) and also how to take care of it. Planning a whole bunch of short rides is the best in my opinion for breaking it in.

You will see that right off the bat, it will have a feeling unlike any other seat youve been on, and despite horror stories of breakin and broken butts, in my case the break-in period really wasnt too bad, hot humid weather perhaps helped, but as a 140lb er, it worked well enough for me.