Excellent write up and advice.  I have been torn between changing my sprocket or staying stock since I do a lot of interstate riding.  I have just shimmed my needles and it helped a bunch.  After this post I think I will be ordering a 15 tooth sprocket.

With everyone debating 15t -v- 17t I guess it's safe to say the engineers got it right with the 16t, best of both worlds. Maybe I'm too inexperienced, but have never felt the GS lacking in torque except above 80mph, and i like the close ratios in the trans so it's easy to always be in the meat of the powerband. I rode some massive twisties this last weekend and most of the way had it in 3rd or 4th. I rarely had to touch my brakes thanks to engine braking and was at the perfect rpm to give it the beans out of the corners (20mph corners @45-50mph) Also, maybe I'm really gentle, but my worst tank of fuel has been 58mpg, and taht was with city driving, parking lot noodling around cones (endorsement test and practice) and my usual 60mile daily commute (highway) I don't know, seems like the stock 16t is the way to go- and it saves lots of time, you just do....nothing!

16 turn does seem to be the best of both worlds.  I am amazed and mpg you guys are getting my best is 50 and average is 48.  Then again I am pushing 280 so its got a load to pull

Does 17t front sprocket with a 39t rear still work with then stock chain length?

Yes.

http://gstwins.com/gsboard/index.php?topic=44849.msg502495#msg502495