I wanted some suspenion too, mainly for general shock absorption, and I tried a few suspension seatposts and found the three I tried lacking. They all felt like something was loose and had a problem with nose wiggle. So I had to put my nicely broken in B17 on the shelf. I got the Brooks Conquest.
I agree about the double rail issue, although there is a device that fits into the rails and allows them to be used on modern seat posts. http://www.wallbike.com/clampvssand.html
The springs on the B72 are supposed to be more subtle. Which probably means less suspension action. I like the dual coils.
On another note, after years of motorcycling in the traditional upright position, I was developing constant severe lower back pain. Medicine, massage, chiro, all did little to help. Then I started riding a "10-speed" bicycle (a drop bar Falcon) and back pain went away.
Don't get me wrong, I have carpal tunnel problems, and I prefer more upright too. I need to have the bars above the saddle height, and get the seat position just right. It took a lot of trial and error to find the right saddle location/bar location.
You'll like the Brooks, in my opinion, and like the spring dampening, but it may not be the solution for back pain if that's what you're having.