As I recall, OEM sprockets are 13/49 = 0.2653
If you go to a 47T rear, new ratio is 13/47 = 0.2766
% inrease in gear ratio can be calculated
0.2766 - 0.2653 = 0.0113
0.0113/0.2766 * 100 ~ 4.1% increase. So if it was going 60 before, it will go 62.4 with the new sprocket at the same rpm. Each gear will be affected exactly the same, by ~4.1% faster at any given rpm.
This is the way I calculate it. Please, anyone feel free to correct me if this is not mathematically correct.
So choose your target and then see what sprockets are available to make it happen. JT sprocket numbers are in the first post:
https://www.chinariders.net/showthread.php?t=32177