18 stam is still 18 stam. You're still not blocking or parrying and since most of your damage didn't come from crushing blows anyway, stam is still a factor. If you need more (when is enough, enough? :P ) then use that one.
I agree that Arcanum of the Gladiator is the best choice for tanking, hands down. I swapped to that when def went out the window myself. That said, maybe I'm a cheap *******, but I wouldn't spend 80g to add just 8 stamina and some resilience to my hat on the eve of the wonderful new world of WotLK.