In XTweak section of XXHE I got 'Time Performance Index': N/A.
From Web search I found 'Command Prompt' instruction to enable HPET:- bcdedit /set useplatformclock true
after reboot and XXHE XTweak refresh I now get:-
'Time Performance Index': Optimal
This worked in W7 even though I do not have HPET option in BIOS.
See http://www.neowin.net/forum/topic/1075781-tweak-enable-hpet-in-bios-and-os-for-better-performance-and-fps/