Also, I find that "load average" can vary from flavor to flavor (e.g. Solaris, Linux, FreeBSD) under similar conditions. This is, I believe, mostly due to differences in process scheduling and memory management.
Load average isn't really a great performance metric.
It is, however, relatively useful for determining if a system is overloaded and something needs an upgrade. But there are better ways to determine such things (vmstat, systat -vm, etc.). Unfortunately, such tools vary widely in availability on different flavors.