According to Mosq's sustained turn list they're both equal in turn without flaps. With flaps the L turns slightly better, but I guess it's well with the margin of error.
The sustained turn performance between the J and L was not in question. It is the ability to move the two planes around in low speed situations that is in question.
It could be the L is modeled correctly and the simulation coding used to mimic stiffer, nonboosted ailerons in the J model may offer a small benefit in slow speed maneuvers.
Again, I have zero proof of any of this so I have no argument with those that say it is bunk.
Delirum's post quoting a WW2 P-38 pilot having switched from a nonboosted plane to a boosted plane suggest the AH simulation is dead-solid-perfect. The question then is why would the nonboosted plane seem to fly lighter than the boosted plane?