For the record, Don S. Gentile had 20/10 vision (he says so in his 1944 book OMAF), but I seriously doubt that was the determining factor in his success. Gentile didn't train with the US, either. Randy, of course, is right: you can't get there from here basing a man's scoring success on his PT experience.
In the spirit of "You don't have to be a dog to judge a dog show" (one of the very
pillars of the Internet, eh?

), I'll say from my own studies that there's something inside a man (if he can avoid getting his tushy shot off by chance in the meanwhile) that will put him way ahead of his fellows every time. I've seen reports from 4th FG pilots that say they had a devil of a time trying to keep up with Gentile as he engaged in combat - he really heaved his plane around;
he put
himself where he needed to be to make the kill. His teamwork with Godfrey came into play as well. He and Johnny Godfrey spent a lot of time working on their one-two punch strategies.
Aggressiveness is another major factor. "Be the Hunter!", as quoted above. Other, lesser-scoring pilots/flight leaders, I'd argue, who flew at the same time as Gentile and the like had pretty much the same initial
opportunities to score, but that 1/10th razor edge Gentile had over his fellows in agressiveness, flying ability, physical strength and other factors like his eyesight of course, put him far ahead of the people flying alongside him in the same type plane and in the same sky. I say the best way to judge the final success of a fighter pilot is by comparing him with his contemporary squadron mates - why in a squadron full of studs do two or three stand out so much, and sometimes WAY above the others?
Ralph K. Hofer (the Frank Luke of WWII) is another great example - in the 'extreme'. He notched up a string of victories when his fellow pilots were getting by with one or two here and there. He had something to prove, or a death wish, but he was fearless, agressive, and determined to kill Germans, and the crosses on the side of
Salem Representative were testaments to the inner man. That, I think, is something that cannot be trained into a pilot. Sure, you can provide the best equipment and BFM skillset, but that core 'fire' is the real determinant.
To end this 4th FG commercial ... be on the lookout for Osprey's book on the 4th, due out next month IIRC. I don't know how many of my picture collection will be in there, but I supplied the author with a CD full!
Wade