couple counter points to pwn.
i'll have to give the overkill some thought, but as far as the video goes:
i don't know if this was determined for sure, but i thought that the guy who made it hacked sc2 to know which units the tanks were targeting, if you have perfect micro, but don't know whats getting targeted, i don't if micro like that can be performed.
second point, with perfect micro i don't think you'd ever use siege tanks vs zerg. you should be using a marine/ghost/medivac army you should be able to micro so banes never hit. without banes, mutas and lings get shredded by marine ghost. You must have ghost in the mix to emp infestors, as this would be the only counter.
marine split for same guy who did the tank vid
http://www.youtube.com/watch?v=DXUOW...eature=related