at this point, you know best about what it might need. You won't screw anything up by adding another washer, as if you go too rich, the bike will just feel really flat at the rich spot with no chance of engine damage. You will want to change it back, though, if you are too rich.
Experiment... there is no set rule about this as every bike differs a bit. 2.5k is pretty low for this bike, though. you actually ride it at that rpm?
Did the shims help with the takeoff smoothness and power at the lower (below 5K) rpms?
let us know your results.
