I think Shires are considered the tallest breed, but individuals from other breeds might grow to be taller. I stood next to Radar and he is impressive. We must always remember that the tallest, might not necessarily be the heaviest.
There was also in the early 1900's, a giant Cleveland Bay who was over 19 hands.
I also spent some time with Big Red, when he was here at our local fair. Great big steer he is. And what about the Belgian Blue cattle and others? Have you seen them? Amazing. I'm still not sure we should be eating meat though, from animals which already lack a gene.
Oh and don't forget, when buying a horse sight-unseen, it can often be noted that they lose an inch or two upon arrival!