@IAmErik .380 and 0.40 both deserve to be on the list honestly. Sadly i was limited to 4, and these are the 4 that are my top picks so I went with it.
As for the importance of caliber... in most situations I'd tend to agree. Even a 0.22 is pretty deadly at close range, at least enough to incapacitate... But there is important differences like penetration potential which can be fairly critical when you consider other factors (like collateral damage).