My attention has been drawn to this one
The link near the start of the thread was to my co-author Emmanuel Gustin's site, not mine. This is my take on WW2 fighter firepower:
http://www.quarry.nildram.co.uk/WW2guneffect.htm
As a result of my analyses, this is my view of the "ideal" WW2 fighter armament:
http://www.quarry.nildram.co.uk/ideal.htm
There are also other articles on my site concerning aircraft gun armament.
As with all aspects of this, the question of hit probability is complex. High muzzle velocity is certainly a big help, especially against fighters. But there is no point in hitting with insufficient force to achieve much damage. In the Battle of Britain, Luftwaffe bombers sometimes returned to base with hundreds of .303 holes in them. And planes got tougher and harder to shoot down as the war went on.
It's worth considering the German and Russian experience. The Germans had two versions of the MG 151 from which to choose: the high-velocity 15mm and the medium-velocity 20mm. The 15mm would certainly have had a higher hit probability, but it was almost entirely dropped in favour of the 20mm which was far more destructive. The Russians similarly preferred the 20mm ShVAK over the faster-firing, higher-velocity 12.7mm UB.