First question: I've read here and other places that critical hits add on average about 50% damage threat over a regular hit for the same amount. I wondered if anyone had any links to tests verifying this (by empirical data from tests or whatever possible). Not that I don't put faith in it being correct, because it feels very much like what I've experienced.

I've tried testing it a little, but haven't really come up with any solid way to verify that's how it works, which is why I ask.

Second question: Playing a fury warrior alt, I don't really have access to all the excellent one handed weapons available in Blackwing Lair and now Temple of Ahn'Qiraj. I've been considering trying to get the Sand Polished Hammer from Ossirian, which has good dps and stats (for my level of playing field). But the hammer is very slow compared to traditional off-hand weapons. So I'm wondering how much impact a slow weapon in the off-hand would have.

The first point I look at is rage gain. If rage gain is based purely on damage dealt, the only difference would be less chances to gain rage from Unbridled Wrath, which I have ditched in favor of Booming Voice, so that would be a non-issue. Some people seem to hold to the thought that rage gain has a flat one rage per hit in addition to the rage from damage, in which case I'd lose a little rage, though hardly enough to impact my fights much I'd think.

The second point would be Overpower opportunities. Here the slower weapon would obviously lose out, but on raid bosses Overpower lights up pretty much all the time as it is now, so I think I could live with a little decrease in this area.

So, after the rambling the question would be: Are there any additional downsides as a warrior to having a slow off-hand?

For the offhand thing, no. We'll have to see what they've done to flurry in the patch however.

A lot of DW Warriors I know prefer having a slower OH since that means their MH will be getting more attacks in when Flurry procs.

Regarding Overpower: You always have the option, no matter the spec, to swap to a 2H and execute the Overpower and swap back. I'm pretty sure that's optimal in any build. :)

Yeah, I know. What I meant was that the faster off-hand hits more often leading to more dodges and thereby more opportunities to Overpower.

I don't swap weapons anymore to Overpower due to the weapon swap delay which is pretty annoying. I do swap to a two hander in battlegrounds when facing rogues and dodging hunters though.

If you're going for DW, then why not the DW set from ZG? ZG is easier than AQ20, and this set is really nice.

http://wow.allakhazam.com/db/item.html?witem=19865

A few other possibilities exist, however.
If you want a really great set though...

http://wow.allakhazam.com/db/item.html?witem=19362 offhand
http://wow.allakhazam.com/db/item.html?witem=19363 mainhand
Is probably the best fury set...depending on what they did to flurry.

I do agree that the swords from ZG are great for dual weilding. Exellent stats and decent dmg.

I use an Edge of Chaos main and a Deathbringer offhand. Deathbringer is 2.9 speed and pretty much your slowest Offhand you can find. I also have 4/5 in offhand dmg talent for the extra 10% offhand. I also have 3/3 improved Heroic Strike. After a charge I never seem to have a problem with constant Heroic Striking and even a Bloodthirst every 6 seconds. After I have my shouts off, rage seems almost endless if you have a decent crit%.

As far as overpower, I'd rather stay in zerk stance to try and keep flurry going instead of dancing to get that overpower. Overpower, in my experience, is more useful to a 2h warrior than a fury one.

I am worried about flurry in 1.10, but I don't think it will be too horrible on a fully buffed raiding warrior. I also think subscience hit the nail on the head with the benifits of a hard hitting slow offhand. Building rage, not consuming flurry hits from your MH and hitting hard are the things you should be looking for in an ideal offhand.

Bottom line, +hit and +crit are your main stats as a fury warrior. If you keep that offhand swinging fast and flurry up, rage shouldn't be a problem with a high dps offhand as opposed to an offhand that is fast with stats.

Personally, I would go EoC mainhand with Ripper off hand if possible, but CTS would be fine as well.

This is the weapon pair that will get me to swap to fury, btw. But that's a while off :D

agreed, i'd take a ripper/cts over deathbringer in a heartbeat.

ripper ? is this something new from AQ ?

Yes. Ancient Qiraji Ripper.