I'm at 1970miles on my '07 M1000 and on my 3rd belt. I never trashed a belt after installing side panel vents and the timbersled front belly pan clutch and rear side panel vent kit. I religiously clean and check my clutches with a scotch birte pad as well as I scuff the sides of the belts too. I don't use any chemicals on my clutches, just scuff them opposite to the belt direction (up and down on the clutch faces). I'm running the 046 cheaper belt, I agree with no need to run the 060. I also haven't touched or checked the alignment since I bought the sled but believe with improper clutching or alignment you will blow belts like crazy, especially at wide open throttle on the trail. I have GPS'd mine at 93MPH without blowing a belt either on the trail, so my clutching is good too. I run the slp recomended front spring, Cutler 64G adjustable primary weights empty with stock secondary clutching.
I had similar problems on my Polaris ProXR 800 snapping belts in half at WOT on the trail, that's your clutches binding. Go back to stock clutching, and do one change at a time to find your problem(primary spring, secondary spring, helix...). If your running stock clutching, check for smooth operation of the primary and secondary up on a stand, you may have damaged rollers, grooved primary weights or the front primary spring catching & binding on the spring cup.