We generally roll with something like this:
Advantages;
- We use 2-3 Shadow Priests and 2 Resto Shamen, so the required slash healing with 9 soakers on each side is fairly minimal.
- Burn movement is straightforward; minimal risk of people spreading to others whilst trying to escape the slash zone. (The very concept of a "grid" layout horrifies me to no end. I envision burning. Lots and lots of burning.)
- Overall healing stability; allowing slash/raid healer(s) to commit a little extra to the tanks when/if necessary.
- Multiple burn targets on 1 side still provides us with a very stable slash group after they've ran away.
Disadvantages;
- Because we have no-one sitting out of the slash groups, burn healing can get a little scary at times; as we often see an excess of unecessary burn damage. Fortunately the slashes fall off before the burn damage becomes excessive; but there's no denying the difficulty in keeping several 3-slash burns up simultaneously.
The soakers at the front are our healers and hunters, removing the potential threat issues of having DPS within the 110% threshold; and also allowing them the opportunity to help out on burn healing if necessary. "Long distance burn running" is also prevented by sticking Mages and Paladins at the back of the slash groups; as they'll shed it and carry on with their role. (We try to promote as much "uptime" as possible.)
In previous discussion I mentioned our preference of 2x Warrior over 1x Warr & 1x Bear; however in our first kill we ended up resorting to the latter; as our Enhancement Shaman didn't show up and we were forced to use the OT's Shaman alt to fill the gap. In an entire night of attempts, the bear died quite often (perhaps 7-8 of our ~16 or so attempts) whilst I only died once. I'm still struggling to determine why we're experiencing so much instability with the bear, yet I'm being kept up with ease.
As demonstrated, the diagram is designed on an 8 healer basis, but pending requirements and composition, we can easily replace one of the Holy Priests with a Shadow Priest for more efficient slash coverage, DPS and VT. We went with 8 healers during learning to provide a little more stability, as we weren't being held back by the enrage timer; rather people dying before we got to it.
I don't know how strongly I'd recommend our method to anyone else as it clearly has it's flaws and is open to alot of refinement. But it does get the job done, at least.