Help! Unlike dishwashers, information on supporting an overhanging marble countertop is lacking real detail.

We have planned on a penninsula with a 42" x 8' countertop of marble. Accounting for the cabinet (24") and 1" overhang on the front, and a 1" decorative panel on the backside of the cabinet, we will have a 16" x 8' wide overhang of marble, counterheight. Thickness is 3CM. According to NKBA, anything over 10" of granite needs support (I could not find a mention of marble). And that support should be at a minimum 1/2 to 3/4 the span of overhang, and for an 8' wide piece, supports should be at the ends and then at 30" for 4 supports total.

I just called my marble installer, and posed the same question to him for suggestions. I have two styles of brackets that we like, but one is 10-1/2" deep and the other is 13" deep. The 13" deep is not our first choice, and is 20" tall, so it will come down on the cabinets a long way into leg room and moving stools around. The other is only 14". Both are solid wood and concave in shape. He felt that granite would be OK with the 10-1/2" support, but that marble is more brittle.

Comments?