I went for two rides this weekend (A new ride, a new rack, and another new ride just didn't sound as good) and installed a new rack in between the rides.
The first ride was yesterday and I did my standard 11.5 mile route. I did it averaging 12.0 mph (I averaged 11.5 mph last time), so I'm getting faster. I knew I'd be close to 12 mph average, so I pushed really hard at the end and was properly exhausted when I finished.
Today's ride was me just getting on the bike and going. This ride was just over 13 miles (which is probably longer than I've ridden in quite a long time - hopefully that will change very soon) and I managed to average 11.3 mph. On this ride, I had a lot of bad luck with lights (e.g., a red light at the bottom of the hill so I'd lose all of my energy and have to climb the next hill from a rest). A lot of the roads were had quite a bit more traffic on them than my usual route, but it wasn't too bad.
In both cases, I got on the Sofrider and rode it without any issues; my body remembered exactly what it was supposed to do. I still have a lot of room for improvement (such as high speed handling and sharp corners), but it's getting better all the time. It's only about six hours after I rode today and I'm already sore in my shoulders. There were a lot of (for me) quite steep hills and I was really working my whole body to get up those.
I replaced the seat post rack with a standard rack (Delta Cycle Ultra Megarack - a nice rack with a silly name) and mounted a tank bag. Since the Sofrider has rear suspension, it does not have the usual rear rack mounts. My idea was to mount it to the seat post clamp.
As you can see from the pictures, I only have one brace to the seat post clamp. The problem is that the nut on the other side of the clamp has a lip with a large diameter, so I'd need to drill out a larger hole on the other brace.
I had this rack on for today's ride. It held up beautifully, but having it link to the seat post clamp means that I have another link from the rear wheel to the seat post besides from the rear shock. I don't think this makes a huge difference, but I'll probably end up moving the braces to be attached to where the rear shock absorber is attached to the frame holding the rear wheel (this will probably involve rigging a simple adapter as the shock bolts are even bigger but I've seen this done before on Sofriders on their forum.