I'd never want to use the name
Horace, but
Horatio is actually my first choice if I ever have a son. There are so many cool namesakes to choose from (though the CSI
Horatio is not one I think of in this regard...not very familiar with the series)!
I like both
William and
Calvin, but I don't think that I'd use either for a middle name in this case.
William is possible because it's a family name, but
Calvin, probably not. I honestly don't know what to use as a middle name for
Horatio.
John, maybe?