I recently upgraded a laptop's CPU to a higher clocked model. The bios recognized the new CPU immediately, of course, but the device manager in Vista (Ultimate 64bit) still showed the old dual cores (T6570 @2.1GHz.) Running scans for hardware changes did not help, nor did updating the performance tool.
I did some web searches (though none too thorough) and didn't find any real answers. I felt brave (don't try this at home!) and went into device manager and "uninstalled" one of the cores of the processor and rebooted.
When the box came back up, one of the cores was labeled T6570 @2.1Ghz, but the other core was now labeled correctly: T9300 @2.5Ghz. I repeated the procedure with the second core and rebooted. Voila! Both cores show the correct name and speed.
If you try to do this yourself, you do so at your own risk, of course. It'd probably be smart to do a backup, but I was too impatient.