The %SystemRoot%\System32\Perflib_Perfdataxxx.dat files are created by the System Monitor. When you shutdown normally, the file should be deleted.
If you have an abormal shutdown, these files can become orphaned, and accumulate on your computer.
Under some yet to be determined circumstances, these files can become orphaned during normal operation.
The best way to remove these files is to add a command in a logon script:
del /q %SystemRoot%\System32\Perflib_Perfdata*.dat