Today, same trip, 'older' '08 bike, 12,500kms. Basically the same set-up, with one 'big' difference:
this bike has a large rear do-nut, Kenda Challenger 140/90-15. Todays result? 55MPG!!!!!
How to explain the diff? beats me. Both are '08s, newer one with 5500kms.
Insurance goes off the older one on the 27th, I'll try another road with both bikes before then, and try to confirm these results.
cheers!