Forgot I posted this, and since another post just got made asking about this, I figured I'd check back in.
Went to the 15th sprocket, JT brand, very nice. I also replaced my chain and went with a cheap one. I might eventually get around to making a new chain guard but I got other projects for now.
The 7500-8500 rpm buzzing in the handlebars is there and worse, way worse. It now goes up to about 9000 which is exactly 70 mph. My right wrist really takes a pounding on the ride into work.
That said, spreading out the gears with the taller sprocket makes the bike a lot more rideable in traffic. You don't run out of gear as quickly and you can actually use the lower gears for riding around rather than having to just click through them. The bike probably could take a few more teeth off the rear sprocket and still be rideable but for now stock rear and 15 front are working well.
I used the same length 106 link chain and it is slightly further in on the adjuster but well within range.
I'm getting a really nasty whine in my final drive from something, either my cush drive carrier bearing, wheel bearing, or output shaft bearing are getting ready to go, hopefully its not the output shaft one, i think that dictates a split engine case...
