As for the convergence issues, if this can be of any help, the Japanese N1K pilots use full 650yds for inboard cannons, and about 300 for outboard cannons.
They use two cannons at a time. The inboard cannons for long range sniping, and outboard cannons for close range snapshots. When the distance is inside 200yds, they use all for cannons.
I'm not sure if they changed their doctrine, since after AH2 and its different gunnery, they seem to be having lower success rates in long range gunnery as a whole. They might have given up long convergence ranges entirely.