Different monitors use different rates. Your video card and any modern monitor will negotiate the rate.
Long time ago with CRT (Picture tube) monitors flicker was a problem and people boosted refresh rates as possible, 85hz was a good target. Some people got headaches from low refresh rates.
With LCDs and Plasmas the technology works differently and 59 hz is just fine. As long as the picture appears you can ignore refresh rate.
Note: (1) Monitors support both digital (DVI, HDMI, Displayport) and and Analog (VGA) connection. The 8400 family supports both, you should be using one of the digital protocols to get the cleanest text (google microsoft cleartext for background) (2) if you have an LCD or plasma panel it has a native resolution, you should use that.