Virtual Domain Cpu Time limit

Question

I'm running Munin on Ubuntu 14.04 to monitor my virtual machines (running KVM, libvirt). I often get a notification that CPU usage on my base system is 'critical':

mydomain :: Virtual Domain Cpu Time
        CRITICALs: total is 2015.19 (outside range [:100]).

At the next Munin poll, CPU usage is back to normal again (somewhere between 2 and 5).

Obviously CPU usage is still fine when it exceeds 200%, since I easily get values up to 2015% (as in the example above).

My question: how can I know which value is actually the maximum my system can handle? In other words, when should I worry and actually get a critical notification? As I'd like to set the notification threshold to e.g. 80% of that value.

My base system is running Intel(R) Xeon(R) CPU E31240 @ 3.30GHz with 8 cores. I expected I could simply use 800% as value (100% per core), but that doesn't seem to be true.