I look after very large environment. We have various performance metrics tools at our disposal. I like to use vCOPS to look into these metrics.
Generally, I have noticed for most of the workload 1 vCPU is good. Adding recourses depends on what kind of applications you are using. I always discourage people from looking at the Task Manager to figure out the correct resource usage.
The best way is to use esxtop and get the metrics. Here is the link to one my article which I wrote some time back - http://vmwaredevotee.com/?s=esxtop
