I'm 5'7", 145 pounds, goofy 18.5" stance, 57/55 on an 18cm waist Donek FC-I 167. Boots are current UPZ RC10 MP26 shells with F-A-S-T heels. I had been riding with Snowpro stepins until I got my Sidewinders just the other day.
This is my first experience with Trench Diggers, and knew that there were some issues with smaller boots, and boots like the UPZ with a short heel. After one day on the snow, I can say that the ride is pretty nice. I have the default yellow elastomers in, and while I can notice the flex while carpet surfing, I don't overtly feel it while riding. For my relatively light weight, I wouldn't see any need to swap in the blues. The slight cushioning effect is a benefit while not creating any slop at all.
I just wanted to mention that in order to fit my boots, I had to use the smallest possible adjustments of the heel blocks. I'm using the insidemost set of screw holes, and both blocks are almost at the limit of their inward travel. The blocks are set so far inside that it is impossible to change the stance angle, cant angle, or remove the binding without first loosening the heel blocks. I find this to be inconvenient because the heel block adjustment is not easily repeatable like cant or stance angle. Just a caveat. Anybody have a helpful hint? If one had a UPZ RC10 of MP25 or smaller, the block-reversal trick might be necessary.