How can a Perfmon "% Processor Time" counter be over 100%?

Solution 1:

There are two counters with the same name:

Process\% Processor Time: The sum of processor time on each processor

Processor(_Total)\% Processor Time: The total for all processors

Your question indicates you're using the first counter, which means that its maximum value is 100% * (no of CPUs).

So if you have 4 CPUs, then the total maximum is 400%, and 80% is actually (400 * 0.8 =) 320% (and for 8 CPUs it's 640%, etc etc)