how to set wuxga 1920x1200@120hz ?

Hello.

Have problem set resolution 1920x1200 by 120hz
or 1920x1080 by 120hz

i have next
1. projector viewsonic ls850wu
2. pc witch ATI hd6850
3. hdmi-hdmi 2.0 cable 5m

the small resolution is work by 120hz but in big not work only maximum work on 75hz

can you help me ?

Thanks a lot.