Got out for very short ride to test the spring. It's immediately noticeable the bike sits a bit higher. I'm a little lighter than Karl at ~230-34 pounds and have been running the two-up setting with side cases and top box mounted but mostly empty or maybe about 1/3 full. After installing the spring I initially set the suspension down to one-up with luggage and the damping at medium +3. This feels just slightly stiff with all the bags empty and I can tell there's a little more reach to the ground at stops. After riding a few surfaces, including a stretch of dirt, I re-set the suspension to one-up, again medium damping +3. This feels pretty good and the back of the bike still sits a bit higher than with the OEM spring.
So in the end I think this spring re-centers the preload settings so that they're actually relevant to me. The rate increase of about 28% is maybe just a tad more than I needed, I think about 20% would be perfect for me but this is much closer than the OEM spring was, so I'm sticking with it. I purposely rode over some speed humps to test the damping (also that dirt segment) and I don't think the spring is overwhelming the damping at all. I felt no need, at least on this short test, to bump the damping settings up to hard. After testing the bike, I think the 10mm spacer thickness is about right.
I can feel the front suspension doing a bit more work now, and before, I think the soft rear was all I could feel. More riding will be needed to determine if I need to do anything spring wise up front.
-Jeff