Item Haste currently does not stack.
My Zerker has the pants w/ 2.0% haste from OOB... Seriously [Removed for Content] devs. If it stacked - i could see it but meh +2%.. I tried using Guantlets of Glorious Speed (+23% haste) FBSS (+15%) and Pants (+2%) and my haste was +23%. So FBSS is now a house decoration 
Assuming the +12 adorn works like weapon damage: At 100% Melee crit and +100% dps you're looking at around (12+12) *1.3 from that +damage adorn so approx 31 per hit. I'm not really sure how the damage is added in.
I think these +12 damage adorns are really good for very fast weapons as their base damage is much lower than the slow 2-h. So if you had a fast club that hit for max 60pts of damage adding the +12 is huge vs the Blackscale at 545+12.
I did notice on the +12 adorn (my zerker has a slash one) it doesn't add to the base damage. When I did /we it still showed the old values so I'm not sure how it adds in the damage... or even that it is adding the damage in 
... reminds me need to look at my parses.
I'd say go for a Mental or Divine damage proc (since we debuff those) for the Maul and the Power Tap proc on the Mace.