Will do on the speeds.
My 2005 got a 16T when I added the 685 and they were meant to be. I ended up with a 16x42 and that is almost 1,000 RPMs less than stock. I can cruise 70 MPH at 4,000 RPMs at 50 MPG.
The 2003 is a 650 and surely it will not like the 16 as well as the 685. I did not have my GPS connected but with the 15 and 4,500 RPMs I would be 65 speedometer MPH. That should be somewhere around 61-62 MPH.
I should be out and about tomorrow and will let you know the MPH at 4,500 RPMs and if there is a performance loss.
Most likely I will install the 15 for the CAN/AK trip.
2005 KLR 685
2015 Yamaha Super Tenere ES, 5/23/2015
2012 Yamaha Super Tenere; Purchased 7/30/2011; Sold 5/23/2015