Load average is based on the processes waiting in the run queue. That means if you have processes that use fractional time slices often you can see a high load average without a high CPU utilization.
The best example of this is mail. The amount of CPU time require to send a message is very limited, but when thousands of pieces of mail are moving around the system (especially if the mail daemon forks processes to handle each one) the run queue gets very long. It is common to see well functioning, responsive mail servers with load averages of 25, 50 to over 100.
For a web server I would use page response time as the primary metric, do not worry about load average. Under modern schedulers load average less than twice the number of cores will usually have no negative effects. You may want to experiment with number of cores per VM versus total number of VMs. Some applications will benefit from many cores on a few machines, others are better at a small number of cores and many instances.