Which operating system are you using? I.e. Windows XP 32bit, or Windows 7 64bit, etc.?
Also, did you reboot after adding that to the registry?
Or, different question: which one didn't work? Adding the "Run at high priority" command to your explorer context menu, or getting RO to run at high priority?
EDIT: I see, it adds the command, but RO is still low priority... hmm.