Honestly I've never tested it. What I do know is that 1H weapons (axes, maces, swords) normalize at a slower speed than daggers. The only reason fast weapons are used for tanking is so we can burn rage faster with heroic strike (and more even white damage to a lesser extent). The faster the normalization speed the less Devastate will do. Basically you are trading devastate threat for hstrike threat. I've never been in a situation where a Hstrike faster than 1.6-1.7 could ever matter.