Quel'Serrar is an EHP weapon, straight up. From what I've seen the threat from Quel isn't that far off of Last Laugh or something abusrd like that, at least for warriors. If you're looking for a threat weapon look else where, though idk how well the 2.0 speed scaling works for pallies.
The major part of Quel, and what makes it better than any other weapon out there at the moment, is the armor portion of its proc. The uptime is around 80%, and for pure physical fights 1500 armor is roughly 5kEHP. Quel should be used for your EHP weapon and thusly you should enchant it with Blood Draining, not mongoose. EHP relies on sets that guarentee additional survival, blood draining is the only enchant that always adds to survival, and gives you the extra HPs automatically when you need it most, especially with AD it rocks for paladins. Mongoose relies not just on the chance that it might be up when you need it for the armor, but also that the small amount of dodge that it has actually makes you dodge an attack when it does happen to be up. Blood draining all the way.
For threat if the PPM increase for pallies is true, then sure I'd say mongoose, though on a less reasonable yet more philosophical level it always seems odd to me to use a BC enchant on a BiS WotLK weapon. Blizz sucks =P
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