Overall 85mhz is a very good setting in all resolutions up to 1600x1200.
I have the G400 and 520GS monitors at this setting. You could do 100mhz but you will probably not notice any real difference unless you game with V-Sync on. Be sure to set your refresh rate at each of the resolutions and color that you typically utilize and adjust the monitor at each resolution change. Windows and the monitor will remember these settings or you could edit the registery.
later....