http://www.yellow-bricks.com/esxtop/#esxtop-thresholds has some guidance on thresholds for different metrics.

Run esxtop, hit the “c” key to view CPU info and compare the usage with the thresholds.

Here are few from the above link.

Note: if your in esxtop you can hit the “f” key and it’ll give you a menu to specify more fields to display.