Super G mode is a proprietary extension to the 11g WiFi standard.
While the router may offer it, your computers wireless interface may not support it. Not sure about your specific equipment, so you might want to check with Apple!!!!
Considering the huge variety of LAN equipment "out there" and the specific conditions where your router is in use, you might find that there is no one right or wrong answer - if it works, great, if it doesn't, then don't bother with it.