Mine came stock with a 4.50x17" rear, and I'm using a 130/90 now, which is a little taller than stock.
We used 5.00x16's (if my memory is right) to build choppers in the late '60's. and they looked huge at the time.
I've had mine pretty well loaded up also, (Vetter fairing, hard bags, trunk, luggage rack, etc. heading out on a camping trip, but I had the middle shocks on at the time. They are larger diameter than the other two sets.
That is probably why the clevis is offset, to allow clearance for the chainguard.
After re-measuring, the ones on the right are closer to 14", and are probably stock size for the K7 & 8's.