HS itself doesn't scale with damage though. If you can get off 13 HS in the time another weapon gets 10, you'll do more threat even if your damage is slightly less.

In a situation with limitless rage:
Warrior with 1200 AP Buffed and Quel: 268 average damage + 157 HS = 425 + 175 bonus threat = 600 * 1.45 defensive stance+defiance = 870 threat * 13 = 11310 threat over 26 seconds.
Warrior with 1200 AP Buffed and Spineshatter: 358 average damage + 157 HS = 515 + 175 bonus threat = 690 * 1.45 defensive stance+defiance = 1000.5 threat * 10 = 10005 threat over 26 seconds. A difference of over 1k threat, and if for some reason you don't have the rage for a HS once, Quel only loses 870 threat by swinging once, Spineshatter loses 1k threat.

Boevis you are right on the formula, i find it hard not to think only about level 60 sometimes.

1st post here but ive been tanking for a very long time.

Boevis wins pretty much. I started tanking in MC long ago with a Timeworn, upgraded from that to Broodlords Defender (yes i suck and never got a Quel), then i used a Crul and now ive been using Widow's Remorse since the first week of Naxx (yeah got lucky). Ive never had the pleasure of getting the TF so being relegated to purples to fight for aggro means you need speed. Crul was great once you HAD aggro, but man i can't imagine using a Spineshatterer, espcially in Naxx. The only time i have any real problems with aggro generation comes now with unlucky parry/dodge/misses on the first couple of attacks.

I would hate to try to hold aggro on fights like Maexxna with a Spineshatterer.