Measuring multi-core processor performance

A client recently came to me with a Gateway GT5082 whose drive he had reformatted and on which he had reinstalled Windows (XP MCE 2005). He told me that since he had reinstalled the OS his dual-core AMD processor was not functioning properly. One core, he said, was functioning at 1/4th the rate of the other and he wanted me to correct this condition. Based upon his description, I could not determine how he came to this conclusion.

I discovered that he had not installed the latest drivers; the system was running on the drivers loaded by the WXP install process. I downloaded and installed the latest drivers, including a recently-updated AMD processor driver.

The system seems to function well and, when I open the 'Performance' panel in the Task Manager, performance graphs for both cores are displayed and the activity of the cores appears to have relative parity (with some variation, of course, as each core handles its tasks).

In an effort to assure my client that the system is functioning properly, I also downloaded CPU-Z and Scannow's 'CPU Monitor v2'.

CPU-Z shows that there are 2 cores (and 2 threads) but does not, of course, display much information as to performance, core-usage, etc. Neither does 'perfmon', which I also tried but which does not display core-by-core activity or stats. CPU Monitor v2 shows relatively even CPU activity and performance for both cores.

Is there a utility that will show usage and performance on a core-by-core basis in a more detailed way than the 'Performance' panel? Does my client have any cause for concern?

Thanks for your time and energy!