Jekyll, I posted the P-51D mod further up in the thread. I know the canvas link did improve rollrate but I'm not sure to what extent. I believe most gains were from 250mph and lower.
I did some looking into the Zeros the US captured and tested, there were only a handfull due Zero's light construction that made it very hard to ship or capture intact.
The evaluation on Koga's Zero stated that the ailerons locked over 200mph (A6M2) and rolling was practically impossible with the exception torque reaction. (Which is probably and exaggeration, but...) This chart doesn't appear to be a A6M2, the roll performence looks to be either the A6M5 with the missing tips(along with a few other mods for testing) that allowed slightly extended preformence past 250 MPH while keeping the same roll performence (and perhaps slightly better) below 200 MPH and degrading turning ability slightly.
The US also added counterweights to the ailerons for testing, and I believe this might be the one used for this chart.