We have a 60" long x 18" wide overhang with our island. Our granite guy said we didn't need to support it, but I beg to differ and supported it just in case. We drilled a 3/4" plywood sheet (just smaller than the entire island)into the top of the cabinets and then routed in 1/2" steel bars (these were also just smaller than the island) and drilled these into the plywood. The granite was laid on top (and glued/epoxied). Although you can't see the plywood unlesss you bend over or are sitting under the overhang, we chose to cover the edges of the plywood with thin strips of wood that matches our cabinets, so it looks like the support extends as part of the cabinets. We did all this because we wanted a clean look with no corbels, etc. It is great (I had to stand on the island to change a light bulb) and I am very happy that I chose to support it...now I don't have to worry!

I know this is not going to help the original questioner posted in 2007 and I sure wish I had found this question back then... But for those of you looking for "THE" answer... hear you go. The Amastin Company, Corryton TN, has been providing steel support bars in supporting hard surface counters to the East TN market since 1995. In this particular case, which is a common one, Amastin offers a 31" long x 2-1/2" wide x 1/2" thick steel support bar that would bump and mount into the back of the front face frame, notch and recess flush across the back cabinet mounting strip. This support would overhang 8" leaving it approx 4" from the counter edge making it virtually hidden. Amastin has the overhang support thing figured out and if you have any questions or in need of custom support advise... Amastin is place to find the answers. Here is a link that might be useful: The Amastin Company- Steel Support Bars

I am not crazy about your knee-wall idea. Then you really have no place to put your legs when you try to sit in that space. Why not just run steel supports parallel to your planned stud wall and cut out the edges of the cab boxes so that the steel supports are flush with the top of the cabinet sides? They will be practically invisible and no one is going to bang a knee on them. As for space, see the top of my island, below. Ours is an induction cooktop, so a lot less heat is involved. We also tend to boil, saute' and pan fry, not high-spatter methods of cooking. Measuring from the back edge of the cooktop (there is a black downdraft behind it that I am including in my distance), we have 19" to the edge of the island where our guests sit when we gather to cook. My sister-in-law always suggests that we have a family brunch at our house when we get together, so we have five or six adults around the island cooking, chopping veggies and sipping mimosas. We all enjoy it. So I have to say that 19" is sufficient for an induction cooktop. I wonder if folks will be sitting at yours when others are cooking, with a much narrower overhang. Oh well, it still makes a good place for the cook to sit and chop veggies! On each side of my cooktop there is about 18" close in, but the island quickly widens and within reach of the cooktop, you get 29" of prep space on each side. On your drawings, you have at least 30, since you have a 30" cabinet to the right. You probably will have an inch or more of the cooktop cabinet that is not under the actual cooktop, plus an inch overhang at the edge. You will have 31" to 34" and should do fine with that amount. It looks like you have a similar space on the other side. I agree that your prep space looks plentiful.

Similar thread recently. Joe posted pics of installing corbels into a cabinet. http://ths.gardenweb.com/discussions/3549316/quartzite-peninsula-overhang?n=11 For overhangs you need to have corbels built into the cabinet or support brackets. That far of an overhang I would recommend corbels built into the cabinet. Might even need support legs honestly. You need to be confident there is no movement, if they do corbels and it still wiggles a little due to the distance, then do support legs also. Remember your considering this a table... tables usually have legs. Keep that in mind.