Brooks B17 imperial or B17 S imperial?

[hebe]

It is a Trek 7.6 FX. It isnt upright but it isnt hunched down, either. The center to center measurement was 135. Didn't measure the outer. So, in light of all that, now what?

From Lovely Bicycle:

For leaned-forward riding: If you are riding in a forward-leaning position so that your saddle is right at or above the level or your handlebars, in my opinion there are only two Brooks saddles to choose from unless you are a very aggressive cyclist: the B17 and the Flyer.

and

The basic rule is: The more upright your riding position (handlebars above saddle level), the wider your saddle needs to be. Brooks saddles come in several width categories.

For upright riding: The B72, B66, B67, B68, and B73 are all pretty much the same, generous width and are all appropriate for a an upright bicycle.

I like the advice above to buy from somewhere with a good return policy. So it would seem to come down to sit bone measurements, and whether or not your handlebars are at or almost at the same level as the saddle. Editing to add, check that the saddle you choose is compatible with your seatpost too.