Part of the reason that data about parry haste isn't wide-spread any more is that Blizzard noticed when tanks really started talking about "parrygibbing" back in BC and did something about it. There, it was a specific problem with certain fights where melee got bounced all over the place, as well as fights where multiple tanks were required to stand in front of a boss together.
Originally Posted by Daiyara
There are two reasons it's less of an issue now--first, Blizzard started to explicitly remove it from bosses that have to be attacked from the front. It's not always there, but it's there a good amount.
More importantly, Blizzard removed crushing blows. That's significant because one of the biggest ways parry haste would splatter tanks was by burning through a warrior tank's Shield Block charges, then hitting again for a crushing blow. That makes things worse than the current situation because you had bosses not only hitting a lot all at once, but hitting a lot all at once and then ending with a really BIG hit.
Because of that, I think a lot of tanks don't worry about it so much any more. It's usually enough to say "melee DPS, make sure to attack from behind" (although most melee DPS are smarter about that these days just in general).
Finally: The best way to be sure about parry haste is to check back on your combat logs, particularly after a big burst of damage kills you. Look for a situation where the boss suddenly attacked much faster when he's parrying several attacks in a row. (Look at the time delta between hits and see if it's smaller than it normally is.)
You can also look up other peoples' combat logs for a boss on an online log parsing site for data before the fact, or if you don't have good data yourself. (Browsing around a bit, I don't see any obvious evidence one way or the other for Steelbreaker.)
Learn to science and stop theorycrapping in its tracks.