Display contours only for filled areas. Outlining filled regions requires less CPU than filling them. Use that when the map slows too much the refresh rate.
When selected, depths values are shown at a high zoom level. This might be useful but can be disturb the map with too much information. Unselect this option to prevent depth drawing.
Some classes are drawing lines using dots or dashes. It can be nice on the display but CPU intensive on some graphic cards. Unselect this option to force using plain lines (also thinner) and release the CPU.