breda 88 looks good? damn!!! i think it looks like a fat lady! best italian a/c in my humble opinion is either Fiat G-55 or SM-79... the SM-81 was seriously outdated, as were all other options in the poll...
It could be pretty deadly if you fired it into a bomber formation, maybe a HE shell? That probably would do substantial damage, but the 37mm cannon on a P-39 could bring down anything with one hit, if it hit it.
If you put a HE shell in a 102mm cannon and fired into the middle of a B-17 formation, you will cause a lot of damage. Or a Flak shell, shrapnel with accuracy, deadly.