[redyaris]

With respect to larger rear wheels, my experaince [on the GS500] is that the bike leans over more, when on the side stand which may lead to problems when parking on soft ground. The other problem is that the rear wheel may not leave the ground when on the center stand. Both of these problems are more of an anoyance than anything else...
your 60mpg plus is looking good. I am stalled by the mountain of small details that I would like to solve by magic but so far no luck.
I will be returning to the original rear wheel size because I don't think it provides any real advantage that I can see. What I have found with the GS500 is that I can't use the lower rpm zone on this engine below 3000 rpm, so the bigger rear wheel is redundant. The extra rotating mass doesn't help much either.