http://www.youtube.com/watch?v=yx6yee5SX3k

Interesting enough... 2 seconds to kill someone as a ele shaman.

A list:

Rogue : 6.3 seconds
Boomkin: 5.1 seconds
Hunter: 3.6 seconds
Demo lock: 7.4 seconds
Shadow Priest: 10 seconds
Ele shaman: 2.5 seconds
DK: 9.7 seconds
Hunter pet alone: 13 seconds