To quote the thread from Elitist Jerks:
"The cooldown on Windfury Weapon means that an OH that is faster than the MH is extremely detrimental to shaman DPS. The fast OH is more likely to hit again after a WF cooldown and therefore has the first opportunity to proc a new WF and trigger the cooldown again."
Despite the cooldown, however, your best enhancement DPS will come from Windfury on both weapons. I tried Windfury MH and every other possible enchant from Flametongue to Rockbiter to Frostbrand, and with the proper selection of weapons, Windfury/Windfury still wins.
Those of us who have been playing Shamans for a while will remember that when patch 2.1 first added the three second cooldown to Windfury, there was a semi-sneaky workaround which basically consisted of putting your max rank WF on your main hand and a lower rank on your off hand weapon. Since this countered the reason for the cooldown in the first place (namely, to make it impossible for shamans to get two windfury procs simultaneously) that workaround was fixed in a later patch.
Therefore, as the thread indicates, you need to try and minimize the chances that your offhand weapon will proc Windfury and keep your main hand from getting the effect of the enhancement, which is not a good thing for your if you are DPSing because your off-hand inherently does less damage than your main hand, and therefore will get less benefit from a Windfury proc.
Checking on WoW Wiki, we can see that Windfury weapon grants the effect of 2 extra attacks with added attack power. Well, if Windfury procs on your offhand instead of your main, then it will be as if your less damaging offhand gets two extra attacks with added attack power - more damage than the offhand would normally deal, yes, but significantly less damage than the main hand can deal. By having the offhand be a much slower weapon than the main hand, you minimize the chances of losing the main hand's windfury procs.
I'm currently using on my Draenei a 2.6 speed fist weapon, the Shekketh Talons as my off hand, while using a Fel Iron Hatchet as my main hand. Before that, I had two daggers as my weapons because they were higher DPS than what I'd brought out into Outland with me, both being 44 DPS or so. But that was a significant and serious mistake and one I should have known better than to make. Unless the dagger is significantly slower than the main hand (and it's hard, looking at Wowhead, to even find a dagger slower than 1.9) then it's going to hurt your DPS. Using two daggers which were about identical was as foolish a move as I could have made, and I can only say that it's been long enough since I was enhancement at this level that I simply didn't realize what I was doing wrong.
It's fairly hard to find a 2.6 speed off hand weapon once you enter endgame. At 70 the most easily obtained 2.6 speed weapon for the offhand might be the Boggspine Knuckles, but those drop in a Heroic, as does the Bloodskull Destroyer. If you're willing to go 2.4 you can get the Runic Hammer crafted, and there are a few more options like the various Gladiator weapons (there are a variety of 2.6 speed weapons you can get in Arenas) but in general the pickings are kind of slim.
A lot of fist weapons that would be perfect are main hand only, and since you want your off hand to be slower than your main, having a 2.6 speed main hand makes that pretty hard to achieve. The Reflex Blades make me cry. 2.7 speed on the main hand, and their matching off-hand is 1.6 speed? Someone hates Shamans. You'd be better off keeping the Mag'hari Fury Brand then using the matched set as an Enhancement Shaman. I honestly wish I could wear the main hand on my off and the off hand on my main, no matter how weird that would look.
This is just a small part of that really excellent thread - I especially recommend the section on totem twisting and the advice on itemization. And as much as I personally love using a 2h weapon, the information assembled here is pretty well convincing that big two handers are inferior for DPS compared to dual wielding as an elemental shaman. It's a generally awesome read and very enlightening if you're out of practice in Enhancement following the past few patches, or are new to the spec.
Next week we'll be talking about Elemental Shamans again, because they need more discussion and love from this column and because I'm finally in possession of enough Elemental gear to really shake the spec down.