My bike also came with 17/42, but I changed to 18/42 when the bike was 6 months old. I think, like myself, most people new to the bike feel the rpms are high when they really aren't. Compared to a Harley, yes, but our bikes have a redline of 7500. With the 18/42 (stock now) running highway speeds 70-80 would be 4000-4500 which the bike would be happy doing all day long.
Just going from the 17 to the 18 I noticed a loss of take off oomph. This is part of the reason I did the big bore. I'm convinced the 18/42 is probably an optimum balance between hwy. and local. I got used to running at higher rpms. The bike performed better with no noticeable loss of mileage. The only way going up a tooth will create better mileage is constant highway running. Having to twist the throttle around town more offsets the difference.
