Viewsonic LCD refresh rate problem

[snappo]

I have 2 Viewsonic VP912b 19" LCDs hooked up to a computer. I have a Geforce 6600 GT video card with 2 DVI outputs and the latest drivers.

I have the drivers installed for the LCDs, they show up as "Viewsonic VP912B" in device manager. I have them running at 1280x1024, their native/maximum resoution.

Their specifications say that their refresh rate is 85 Hz at that resolution (link) . However, when i go to Display Properties->Settings->Advanced->Monitor it shows the refresh rate as being 60 Hz. That is the only refresh rate I can choose. The "Hide modes that this monitor cannot display" checkbox is checked.

How come I cannot select 85 Hz. Would it be safe to uncheck "Hide modes that this monitor cannot display" and raise the refresh rate? When I do uncheck that box, I am given the options of 60 Hz and 75 Hz. Still no 85 Hz. Why is this? I am very confused. Thanks a lot for any help.