My 2001 W650 still had the original tires on it with 4500 miles on them. I ride a lot of gravel roads in the mountains of Western North Carolina where I spend the summer. Always had good luck with Avon Distanzias so I ordered up a 100/90-19 and a 120/80-18 and just installed them today. The rear 120/80-18 is the same diameter as the stock 130/80-18 according to both manufacturer's websites and actually the new tire was a little larger since the old tire was worn.
Just took a short test ride and the bike does feel different but that is probably due to new fresh round tires vs 12 year old hard flattop tires.
Note the highway pegs that I got from Bruce P. Very nice to have a another foot location on long rides.
Also I did the 3.5 turns out mod on the carbs a month or so ago but my MPG dropped from 60 to 55 so I went back 1/2 a turn in. Still seems to warm up faster and no popping on deceleration. I'll check the MPG for a month or so to get a new reading.
Edit: Just got back from a 70 mile ride out to the country and all is well with the handling with the new Distanzias tires.