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.

Thanks for your responses. Mindimoo, your steel structure is awesome. No worry there. I wish I had researched this much better before having my kitchen demoed and ordering the granite. You both have some good points and good questions. My granite is 3 cm. It is black (Labrador Angola) which I am told is the strongest of all granite because it is much less porous than the lighter colors. The steel rods are threaded and they are imbedded in the bottom of the granite, covered by epoxy. So, water isn't an issue. There are 5 rods total. I don't know what it's called or what size it is. Looked like 1/4 to 1/2 inch. They say it's made for granite and the concept is similiar to what is done with concrete. One rod is in front of the cooktop cutout. One on either side of the cooktop extending to the 13" overhang, and two on a diagonal to each corner on the other end of the island which is where the 15" overhang is. These two probably don't meet the 2/3 to 1/3 rule. My original plan was to do something similar to the picture above in plywood. When I contacted my Lowe's cabinet installer to say I wanted to go back to Plan A he said it was overkill. He says he has demoed numerous kitchens where they had used the steel threaded rod and it is really difficult to break the granite. He was confident in their approach. I like and trust this guy but he is super busy so I hope he wasn't just telling me this because he didn't have time to help me prior to the install. Anyway, the granite was installed today. The fabricator gave me a written warranty that it won't crack as long as we don't sit or stand on it. I still have mixed feelings about the support. I still have the option of putting corbels on the end of the island although I wanted to avoid them because they are tough on the knees. But then again I wanted 15" there for the extra leg room since that is what many seemed to recommend on this forum. Also I could have L brackets on this end. There are doors on both sides of the island but the ends will just have panels (fake doors) which can be cut or notched for corbels or L brackets. I'm thrilled that the granite is finally in. I've been 2 1/2 months without a sink. I don't want to regret not researching this more than I did or rushing into things. If only I knew about this forum sooner. The feedback has really been great! Please let me know what you think. Thanks again!

Without a support, your overhang is going to be a cantilever. The rule of support is that for every foot of cantilever, there should be 2 additional feet behind the cantilever end that provide support. Therefore, to support an overhang that is 2 ft wide, you need to have 4 ft of island behind it, at the minimum. If you already have total 6' island dimension, no worries. But if you do not, either use brackets or decorative legs that will provide anchor to the floor. Legs come in all styles and shapes/sizes. Hope this helps!!

The polished Pental quartz was installed today without any glitches. 🤩 The Youngstown cabinets have steel bases and they screwed right off. There was enough to do the 48” vanity in my upstairs half bath. Tomorrow morning the plumber returns to put in the new faucet. Depending on the light, this color quartz is “moody,” which I love. 💟 Next, the bathroom gets painted and it’s done. The kitchen kept its “retro” vibe.