Might download the free version of SiSoft Sandra. Pretty good synthetic benchmark suite with a lot of breakdown on system usage. Might help pin down a problem area and see a difference between the two rigs.
Maybe also check bios settings. Maybe the slow rig isn’t hitting boost frequencies on the processor?
Are you sure the settings in RC are identical? Maybe do a <Shift> launch RC on both rigs and reset both for testing.
Last resort… threaten to fire the slow rig for laziness.