Harvey has it right I believe.
Use the "same as desktop" setting in the refresh rate overide in the Catalyst drivers.
*Set your desktop to 85Hz, and adjust your screen if needed at that resolution.
*Switch to another resolution you want to run on your desktop, set the refresh rate to 85Hz and again adjust the monitor settings.
*Do this for all the resolutions you will run, making sure you set the refresh rate to 85Hz.
You can check to verify that your monitor is running the proper refresh rate using the monitors OSD menu during games ect.