I have one of those Topeak bags and it worked from my stock saddle to my Brooks B-17. If you look at the Selle SMP you can see it has long rails for the quick release to mount to. I had to scoot my stock saddle back a hair to get clearance and my Brooks accepted the quick release with no problems. Looking at the length of the rails it should fit, the width of the rails is somewhat standard. When I had the bag mounted to my Specialized the rails flared out a bit at the back but the quick release still fit. Based on my experience with one bag and 3 saddles I think you'll be ok.