- If I ever find the right saddle and it actually be completely comfortable? Will angels sing and the sun shine on me through the rain? It's okay if it won't be...I just want to know where to set my sights.

Yes, and yes For me it was very much an "aha!" moment - no more PAIN! Like a miracle. I tried a bunch of different saddles and there were a couple that I couldn't fathom getting back on after the first ride - those were pretty easy to eliminate!

- I measured my sit bones and it's about 160mm from outside to outside, and 130 from center to center. Does that mean that I need to have a saddle that has a flat spot that's 130mm or 160mm? Or something else?

Honestly, I don't know.. I would imagine it's somewhere in the middle.. maybe not exactly, but I would venture that it's different for everyone because we all have different pevlises. I recently measured mine inside and outside off a pevlic x-ray, and my 168mm falls in the middle... more to the outside than inside. Obviously that limits my options quite a bit.. but I love my Brooks

- Also, if I ever find the right saddle, will it still be comfortable-ish after 100 miles?

Absolutely. It will be the last thing on your mind after a long ride, once you've found the right one.

- And by trying out too many different saddles over a short period (a month or so...300-ish miles), am I messing up my butt tissue so I won't even know if I find the right one?

Honestly, I don't think so.. if I had continued to ride on some, before looking at something different, I actually fear I might have done some permanent damage. So I don't think switching quickly is a bad thing - as long as you've given yourself enough time to know you don't like a saddle or that it's just not supporting you how it needs to... most of those issues don't get better. The once exception is if you're experiencing some sit-bone soreness for the first time (for example, if you were previously being supported only by soft tissues).. that can take a couple of weeks to fade away, just as it would if you are returning to riding after taking some time off... however I've never found that sort of "soreness" to be anything more than mild.