I built a 60” wide low cabinet for my audio video equipment. Loaded it is incredibly heavy. Started with just 4 outside corner legs securely fastened. Cabinet is 3/4” plywood edged with 2-1/2”oak on all faces with solid oak top and rigid back. Still sagged over time - took about a year to fully sag. Ended up adding 2 casters to middle for support and easier mobility and that cured it. Can not believe a cabinet even wider would not have serious issues.