For large overhangs, the best choice is steel, or to build a "table" with stretcher bars and legs.

If your overhang is 10 inches or under, you don't need support. But, don't let your kids sit or hang on the edge too much. If you want to keep it clean without knee knockers or poles, try those steel poles/bars that will go across the underneath. I believe that they are sixty a piece. They are attached across the actual cabinet and you won't see the slim piece of metal under your overhang.

It's some sort of metal pole. I can't remember what it's called. I'm sure someone else will chime in. I called lowes and they gave me that price. You can find them online and install yourself too.

Our overhang is 10 inches. We haven't had anything larger ever, so we don't know any better. We put in the same length quartz as our old laminate. I believe that most people have at least 12-15 inch overhang, though. My barstools fit about 3/4 of the way underneath. So, it's fine for us. But, our knees do hit the cabinet if we don't back up enough.

Something to think about. :)
Good luck!
Kim

Check out this website which deals with all different types of granite support devices.