He might be the best sub 6' headed goalscorer to ever play. Who else is even close? His aerial ability is nothing short of miraculous.
I agree but Dax would like a word. More seriously, Griezmann comes to mind at sub-6' but Cahill has obviously done it for much longer.
Ivan Zamorano's wiki page claims he was 5'10'', which sounds wrong, but he was also amazing in the air.
Klose was much better than his 6'0 would imply.