I was actually thinking about something however. The problem with the LFR version of Gurthalak is basically you are giving up higher self-damage from Normal Sulfuras for higher overall damage with the proc included. LFR Gurthalak is a clear winner, as the worst Gurthalak parse is equal to a higher end Normal Sulfuras parse.
I had an idea about how to basically have the best of both worlds. The highest value-point where Sulfuras outshines Gurthalak is during our cooldown phase. At this point, our 3.8 speed weapon clearly outshines the 3.6 Gurthalak if you do not include the tentacle spawns. However, over the course of an entire fight, Gurthalak will do more damage. So my thought is:
WEAPON SWAP MACRO.
Have your cooldowns tied into one button, with the first sequence of your "I WIN" button as /equip Sulfuras, the Extinguished Hand. Go through your entire cooldown rotation, and when Avenging Wrath/Zealotry wears off, weapon swap to Gurthalak to take advantage of the tentacle proc producing higher overall dps. When you get back to your cooldown phase, activating your cooldowns will re-equip Sulfuras, you will gain the entire benefit from the slower weapon speed on the part of our combat rotation where weapon speed matters most.
Weapon swapping the LFR version of Gurthalak and Sulfuras may calculate out to higher dps until you get lucky and get the normal version of Gurthalak, which will easily outshine Normal Sulfuras.
Just an idea for those who will have poor luck getting DW to spill his tasty loot!!