50-90 Hz is often a safe setting for SVGA monitors. On both settings, the high number is the one to be concerned with. Using a setting that is beyond the limits of your monitor can cause damage to older monitors. Newer monitors often have protection circuits built in to keep this from happening. The type of video card you have.
Video cards are fairly easy to figure out.
Usually the video card model or chipset is printed on the side of the card that you have. However, if it is not, most BSD systems can detect the type of card that you have during boot up. You can start X manually, using the command startx or you can setup a graphical login using xdm . You can edit this file if you need to specify any special runtime parameters. When X is started via the startx script, it reads the file .xinitrc from you home directory to start the Window Manager.