There are a lot of HA failover capacity calculation blogs out there. The most apply to virtualcenter2.0.1 not to 2.x.
Virtualcenter 2.x (and 4.x) uses other calculations than virtualcenter 2.0.1. if you are still using version 2.0.1 use the following blog at vmwarewolf. For virtualcenter 2.x there is also a great post at virtualgeek , based [...]