Found this old thread that's been partially resurrected, and wish to comment.
When I had a G650X, I found that different riders had different gearing preferences. 14, 15, 16, 17 ... (15 was stock on the Challenge, 16 was stock on the Country and Moto.) I found that a 15 on my Country was a good fit.
Four weeks ago I traded my Country for an F700GS. My first start on a dirt apron told me the stock 17 was all wrong. Yesterday I installed a 16 and am much happier!
My point is this: EXPERIMENT! Countershaft sprockets are relatively inexpensive and can completely change one's perception of one's bike.
Fuel mileage? Never saw any difference between a 15 and 16 on my 650.
Buzzy at freeway speeds? S-l-o-w d-o-w-n. You'll arrive at your next gas stop 10 to 20 minutes later. (A friend with a KLR calls it matching one's expectations to one's bike.)