We've got him down today (just two hours ago), and as you guys said here, the key to reach the hard mode timer was to move more people from the arena to the tunnel, finishing with this setup:
1 tank, 11 dps, 1 healer (tunnel)
1 tank, 7 dps, 5 healers (arena), except tonight, where we were running 1-8-4.
And every time we were getting to Thorim with around 20 seconds to spare.
In phase 3, our biggest problem wasn't either dps or tank survivability, but raid positioning. In some trys we'd wipe at the 50-85% range due to ranged and healers not being careful enough or not paying attention to Lightning Charges and being too spread between eachother.
We solved this last bit sorting the ranged dps in small camps (2-3 dps and 1-2 healers, 4 spots around the room with a maximum of 4 people in each group) and we got our kill (it was rather messy, mind you, since both the OT and me died at around 8%).
As for the tunnel, I went with the method I've seen explained in the forums. Picking just the Iron Guards and leaving the healer to the DPS, as soon as the remaining add is at 60% or below (or both of them at 40% or below) I go ahead and pick the next group, rinse and repeat, picking the 1st miniboss. For the stairs, we kill first the 2 healers and DPS finishes the 2 melee adds while I run upstairs to pick the 2nd boss. Sometimes we were getting an additional add, but we were still comfortably ahead of the timer.
Oh, and in regards to the MC tactic. I didn't really consider it as I wanted to check first if we could pull phase 3 by ourselves; it was our spriest who actually brought it up after checking himself on one try the performance of the add. He liked the Warbringer's DPS and there was no way we would stop him from MC'ing the guy for the whole phase 3.
All in all, thanks for the tips, it's been really helpful for our Thorim's hard mode kill