After reading the very interesting thread in these forums about the aggro generation of Thunderfury my guilds MT started using the sword again after a lengthy time in the bank gathering dust. I am the guilds main offtank and have always used The Annihilator due to its sunder stacking bonus which does indeed help a bit with damage.
Whilst offtanking Chromaggus I was able to pull the aggro off the maintank after two minutes of fighting, we both thought this was strange and sought to investigate our findings.

Here is what we found:

Using KLHT threat meter, myself and the MT went to Blasted Lands to take on the unkillable Giant - a fair fight as we could generate infinite stats.
At the same time we started Proc Watch to accurately work out the frequency of each weapon's proc.

Fight1: MT started building aggro for 30seconds before I started. At a rate of 19% procs he held aggro for 1min 24seconds before I took aggro with just auto attacking and a proc rate of 29% on my axe. KLHT threat meter pointed to threat generation well above my white damge.

Fight2: I began the fight this time, again for 30seconds before the MT started. My axe was ona proc rate of 27% this time with the thunderfury reaching just 17%. I never lost the aggro on this fight and once again KLHT showed a significant amount of threat was generated by the axe' proc.

This probably isn't conclusive but it is certainly interesting and has made our MT rethink his TF usage.

Indeed but he will be in 6/8 dreadnaught withina few weeks which will give him the 440 defence and high stam he needs, it does seem to defy belief that a blue is so good though. Oh Praetorian he was using Bloodlords defender instead as he took a defence loss in other item slots In AQ40.

You misspelled the weapon's name.

Annihilator (41.5 damage per second)
Chance on hit: Reduces an enemy's armor by 200. Stacks up to 3 times.

It seems that chance on hit has a lot of threat.. Maybe Blizzard thought no one used it (never seen it been used), and so never noticed that the proc has a lot of threat with it.

Another interesting argument I forgot to add is that although the mob attack speed reduction of TF is awesome we ended up making on of our 5 DPS warriors use 5/5 Conquerors to amke thunderclap a 15% speed reduction. This when you consider TF is a low 15-20% proc chance is far better for heal rank2 spamming guilds as it keeps a constant reduction in damage as opposed to a proc reliant 20% reduction.

Thanks for the spelling help too:)

http://wow.allakhazam.com/db/item.html?witem=12798

wow ive never heard of this weaopon before, looks like a very nice tanking weapon for those fights where you need damage not survivability
-600 armour, sounds pretty hot to me, i notice a big difference when CoR is on. Patchwerk offtank might be a decent spot to put this weapon, our MT just got widows embrace tonight, might get this and see how it fairs.

I don't get it.

I dont mean to be rude but this is not the way to dispute someone's test results. We really need someone else to try this out and get a larger sample.

Well, if it really is about a 30% proc rate and the debuff is generating ~200 damage worth of aggro, it's generating an average of 60 extra threat per attack. That would be quite a bit of oomph for a blue.

My issue isn't the fact that Annihilator possibly generates more threat due to an abnormally high procrate -- as Gurgthock mentioned, it's the fact that you would bank TF and/or use Annhilator in place of it regardless. Is threat generation that big a deal for you that you need to use this?

Wodin: Forgetting about the minor stats on TF, giving up a 20% slow and using a ~41DPS weapon in place of a ~85DPS one seems a bit odd -- unless as I mentioned you're really having aggro issues to the point that you need the relatively marginal improvement that Annihilator would give (supposedly).

To the OP: Are both of you spec'd the same? How about gear? Additionally, was this just over 2 fights or have you done anymore extended testing? From everything I have heard up to this point the proc rate on the axe was quite low, so 30% is surprising.

Even given the ~30% proc on that axe, I find this more than strange

Could you do the simple test of auto-attacking until the proc goes off once, then having someone else auto-attack until they pull aggro. Getting the exact amount of threat that the proc causes would help quite a bit in analyzing the weapon.

I think you should test on a mob that doesn't mitigate most of the nature damage from the TF proc.