fishboat

+15, +20, +25, +30 & the Oz thing..It sounds like they break it down into a more exact science than it really is..or ends up being. I don't think your butt liking a saddle is going to be that predictable. While 20/30-somethings doing time trials, triathlons, and dedicated racing is a thing all to itself and excluding the casual once a month 5-10 mile rider whose butt nearly always hurts as every ride is like the first time....the rest of us just ride bikes. And most of that time we ride very much the same. Make a good estimate for how you ride most of the time and jump in. If it happens to be a leather saddle..buy a good condition used one(it should look new). It(you) may or may not need a break-in..for every person that says their breakin period was 500 miles, there's someone else that needed no breakin time at all. Ride the saddle for 50 miles..if it's comfortable, then ride a few more days back to back at 50 miles each..you'll figure it out.

Things can change over time also. I've been riding for 40+ years. Nearly 30 of them were on Concor saddles(140mm wide) and I picked a Concor when they first came out for one great reason (when you're young)..I liked they way they looked. It was comfortable and I never gave it any thought. One spring years ago it just didn't work any more..and the search began for something new. After a half dozen saddles that were "technically" right for me, but in practice weren't, I figured I'd try a Brooks..and my search ended.