On a PC, there are a lot of other things that effect performance than the SAS procedure itself. Some thoughts.
PC performance degrades with time. Microsoft and other applications deposit things on the PC that effect performance. For a level playing field, the PC's should be re-imaged.
McAfee On Access Scan sucks resources. It is particularly noticeable when first running SAS. McAfee checks all those little DLLs before SAS can first use them. Again, for a level playing field, either turn off the OAS for the SAS Program Files and data sets or re-boot between tests.
Defrag all the disk drives before starting the tests.