The CPU utilization line is the CPU utilization of just the browser process that is running the test (same as you would see in task manager) on a fixed scale from 0-100% (sampled in 0.1 sec intervals).
Usually if I see something that looks suspicious I’ll load it up into Dynatrace Ajax Edition (great free profiler for IE) and run the page through to see if anything jumps out. I’d love to integrate the capture of the profiling data at some point in the future.
Even though it wouldn’t really impact the numbers, right now only one test is ever executing on a given machine at a time. We can (and have) run configurations with multiple tests at the same time but when video capture was introduced it killed our ability to run in parallel. I’m experimenting with running the tests in VM’s to see if I can get more testing capacity out of the hardware because the machines are pretty beefy and could easily handle 8+ tests in parallel but I won’t do it if it introduces any variability into the results.
Hope that helps,