Funny I had a similiar experience two days ago; although somewhat in reverse in terms of bike types.
I have an NOS 2002 Trek 520 which had a nice narrow little racing seat (On a touring bike..gimmie a break Trek). I gave it a shot a few times, & hadn't gotten 'round to getting something new yet...after a 6 miler not using bike shorts with my wife she determined she wanted to go do another longer shot which I was up for, but since we were passing home, I yanked the seatpost, brooks & all out of my Jamis, & did a quick switch. Even though the bikes have very different geometry the subsequent ride with the brooks being the only change was a slice of heavan, no soreness no nothing. I suspect Wallbike will be hearing from me shorly; although I'm considering a Selle Anatomica like my wife has.