The DMG/Defense/DMG/Defense works great against these Full S3 teams rushing us up and coming "Ellays."
There definitely is an art of using our burst dmg with the 4X shaman setup. I find that finding the softening up the target with Purge pays huge dividends! Being able to soften a target up, check to see what kind of healing attention theyre going to get, lowering their dmg, and having them potentially blow their Defensive/Offensive cooldowns is priceless (Mages Iceblock real fast after getting hit with purge...). Using purge has really increased my Dead Target to Nuke ratio to around 95%. As long as you drop that first target it gets much easier from there. Heal through their damage, toss some more purges around and find that last target.
The Last target is usually standing right in the middle of the arena, they've long gone into tunnel vision while trying to nuke you down, and you let them have the old Lightning Bolt, Chain Lightning, ES combo. Against a 2 or 3 healer setup Im OOM 99% of the time at this point in my fight. The great part of the DMG/Defense/DMG/Defense strat is now they have at most 1 dps up. I work on regen and heal as necessary, with one dps its laughable the amount of dmg they can do with 5 healers. After regen (It still tickles me today that shaman have regen after playing them before the expansion, OOM use to mean Game Over!), sometimes my NS+EM+CL is up again and I enjoy punishing the last DPS target, and 99% of the time the Healers leave the arena. Some important things to remember are to try and kill the DPS in LoS of each other. This allows you to make sure your searing totems are up and you're stopping the potential rezzes.
Mind you I feel kind of bad for the other team, but after waiting for them to zerg for 5 minutes I do get an evil grin knowing I've got it in the bag!
I'd Say my wins aren't nearly as clean as they need to be. But if anything at all its supporting Ellay's theory that killing the DPS first leaves them with almost zero options to Win the match (watch those rezzes!).
So I'm sure I haven't told you anything you didnt know, but hopefully I've helped share with the community what works for me.