kevdp4- It is interesting to me that you bring up that many fabricators do not do miters. I am finding our fabricator is very resistant to mitering. When I brought it up her excuse was- "well it's too expensive so nobody does it so we don't do it". Yeah. I'm a bit frustrated. Our kitchen is a new construction build so I'm fairly locked in to this fabricator as our builder's preferred vendor. I'm more than a tad nervous, however my designer insists that they've never had a problem with this fabricator in the 6 years she has been working with them. They were also resistant when I brought up (after Trebuchet's advice) doing a 1/2 radius on the sink edges to reduce chipping. Same response about "too expensive, we don't do it" Well that's crap because a 1/2 radius is a STANDARD edge option with them. So I don't get it. Is that kind of edge option really hard in a sink vs on the counter edge? How does a positive reveal of a sink affect doing the 1/2 radius at the sink?

My onyx counter is a 2cm slab with no underlayment (you would always want an underlayment with any other stone though). I have an oge edge on the onyx and it's quite lovely. I didn't want to build up the edge since it's goal is to appear to be more furniture like than cabinet like (if that's possible). And I've seen bad onyx edges that show because of the underlighting so I wanted to avoid that. I think the edge is lovely, and have no regrets. I have a mix of 3cm and 4cm thick counters throughout the house, and each fits in the space it was designed for. I think if you design well (ie not like that hanging chad in Blue's old kitchen) 2cm without a built edge would be lovely. Do NOT be tempted to skip a support system though. My onyx counter has very specific rules attached which you would not want in a kitchen. For instance, we can't stand or lean on the middle of it, and shouldn't put heavy weight on any edge (so we have to brace it to hang the curtains before we can get close enough to take them down or put them up). And to put a sculpture on it, we have to add a support collum in the middle or it could crumble into nothing. Only 2 year olds are allowed to dance on it (and they do with great joy). You don't want to limit dancing on your kitchen counters :)

Unfortunately I didn't take any photos when I saw the slab here in SoCal. But, I don't think I would recommend the New Carrara. The slabs have been coming in quite gray. AZ tile will admit it. We were deciding between New Carrara and Calacatta Zeus. The 12" samples we got made us think for sure New Carrara veining but when we saw them in person, Calacatta Zeus was actually really lovely. Bigger movements of more subtle light grey veining. Carrara was a lot more activity with all over swirls. And again, very grey. We did slate colored lower cabinets and so happy we got more contrast with the white countertops. It also matches very well with our white upper cabinets. That all being said.. I don't see Calacatta Zeus on Arizona Tile's website any longer. I know there have been issues with the tariffs being put into place, but if you can grab some slabs, do it!

"Does anyone here have anyone experience of opinions on this?" Yes, about 30 years of experience. You've got something that can't be built as designed without some tradeoffs. The 10' span with the 9" and 11" overhang on each side must be supported in a way that does not allow the stone to sag at all. If you disregard this advice, your miters at your waterfall will self-destruct. That is required by the laws of physics, not the building code. A sagging top is longer than a flat one and the only place that length can come from is as a gap at the top of the miters: There are many ways to give the top the support it needs, but that's going to require some esthetic tradeoffs. I would like to see a custom steel frame incorporated in a manner as inconspicuously as possible. You and your crew should be able to sit on the substrate without sag. Imagine your 2cm top as a veneer over this frame. You may have to install some panels perpendicular to the wood veneer design panel. No matter how you get it done, you must get it done. The GC's and the fabricator's checks will have cleared well before the miters give way. Gravity works slowly but inevitably. Any rod had better be imbedded in a remnant and backlit first. Imagine turning on your lighting for the first time only to have the reinforcements screaming at you through the top. This is a real possibility particularly with 2cm stone in a lighter color. May happen in plain 'ole daylight.