I've used the sp a lot as well . . . agreed that one backup not works well and is mandatory if you are not caring the rope (the weight of the rope cinches the clove hitch). I usually use about a 30-50ft loop between the knot and the device. I prefer to flake the rope on the ground if doing single pitch (less weight) and carefully stack it in a sling/bucket if doing multi-pitch. 10.5 has worked well for me in the past. I have used it for lowering as well, although not ideal, it does have enough friction, for short lower outs. If rapping a full pitch, I'd recommend a Gri-gri single line (assuming multi-pitch climbing). Also . . . don't know if they're still made or not but 2 Petzl williams spin ball biners, connected through your tie-in point works well. Screw gates loosen up as they rub together and auto-lockers are a pain. With spin balls both gates open in unison and they stay locked. Finally . . . regarding the 2mm, (assuming I am understanding you(spotly)). . . just tie a butterfly or figure eight into several pieces as you move up. That way you are constantly building a bomb proof anchor as well as reducing the chance of slack building up on the anchor side. The catch is pretty soft with the sp, I don't know the KN, but it feels pretty soft, not sure a screamer would be that beneficial. Oh ya, don't grab the rope if you fall, you will fall a lot farther and probably get some nice rope burn.