X Japan might be my favourite band of all time but "I.V." definitely doesn't represent their best stuff (especially so for the drum parts!) since it's a post-reunion song. If anyone is interested in checking out more from them, check out the first two albums "Vanishing Vision" and "Blue Blood" back when they were just called X.
And for the song with the best/most diverse drumming I would say check out the song "Dahlia" from the album of the same name.
David's comments