"Fast weak.." stopped reading there. Wouldn't say them "weak" as I've critted 14.6k to a DK with AMS and full PvP gear, I think some of the RNG's DKs can confirm this (LOL!)
Obviously, you should go for intellect / haste depending on your arena team. If your team has good survivability (eg. healers), go for intellect. If you however, trust on fast burst - obviously go for full haste.
You guys who are saying "intellect, intellect, intellect", forget the fact a mage gets insane damage buff by doing 3 ABs in a row, and you get there faster with haste