I am new to this forum, but not to the KLX
I have a 05 KLX250/300 and have used a number of different gear ratios.
I am now settled on 13/46 with a 108 link chain.
This gives me the most options to change ratios without a new chain.
I can run 13, 14 or 15t fronts with this back sprocket.
That said, I have found the best ratio for trails on my bike (remember it is a 300) is 13/47.
It will lug slong in third gear at slow speeds on this ratio – my bike has a few mods and very good low down power.