Usually an island that is not moveable with casters is considered built in and requires electrical be installed which can only be an island thatis properly installed. BTW no idea why this would tip since it is not larger that the base . I would not do a 40" high island it is neither bar height 42" or counter height so just awkward IMO. As for the counter making it tip with no overhang I see no way for it totip other than if you opened all the drawers on one side at the same time. I have 30 x24 " stainless cabinets on casters with large drawers filled with heavy pots and i opened both drawers and the whole cabinet tipped forward so be aware of thst But IMO if you sre not making this moveable why not attach it to the floor and not worry.I run a catering biz from my home so those cabinets i mentioned are meant to move where ever someone needs a counter outside the busy kitchen

Yes, it’s a tip over hazard when a ”mobile” piece has a top is heavier than the base. You’d want to weigh down the base with your cast iron and cement block collection, and a lighter weight top than 250 pounds. The base needs to outweigh the top 2/3 to 1/3 for anything ”mobile” So you’d need 500 pounds of base for that to have a 250 pound top. And now it isn’t mobile. So you might as well just fasten it down properly, and add the required electrical outlets.

No it's not a tip hazard. You need a cantilever for it to tip over (you need a vertical load outside the supports), and since you have legs on all sides that (presumably) touch the floor, there is virtually no way for this to tip unless someone tries to use it for squats.

Just think of dining room tables. No one is ever concerned about those tipping over, and plenty of those have stone tops. I'm not sure if there's some odd code thing that requires mobile islands to be designed as bunkers as Verbo suggests, but the laws of physics state otherwise.

If you were cantilevering your counter, that would be a different story.

You have to counteract human behavior, not human intent. Just try scooting something heavy along, instead of rolling it, with all the weight at the top. People don’t push against the bottom, where they should. They push against the top, where the weight is located. Over it goes. Tables are large enough that they require 2+ people to move.

If you intend to do prep work on the “island”, 40” high is too high unless you are unusually tall.
To eliminate any possibility of tipping over, have it attached to the floor and have the top glued to the island. I’d include an electrical outlet so you can use a hand mixer or other electrical hand tool. If you have cabinets instead of drawers in the island, it is not likely to tip over. Children have been known to use drawers as stepping stools to reach something they want, and that’s the danger here. Pulling out two upper drawers at once can tip the island unless the bottom drawers are loaded with your heaviest things. Don’t take a chance.

I'm sorry, but whoever says a 4'x2' island 40" tall with a stone top is not a tip hazard is not thinking clearly. Of course it's a freakin tip hazard. A dining table is not 40" tall and it's not just 2' feet wide.

Ok just for fun. Because I'm an engineer and like math. 
The maximum recommended push/ pull force for workers is 50 lbf (osha). So assuming someone is really trying to push this thing over, we'll use 50 as the lateral force exerted at the top. 
The weight of the slab and the weight of the cabinets both resist this force. In order to tip it over, you'd need to push on the top to overcome about 1/3 of the slab weight and 15% of the cabinet weight along with whatever is in it (assuming you push from the free counter side... if you push from the cabinet side, it would be 50% of the cabinet weight). The slab is about 160 lbs, so 1/3 of that would be exceeding the safe force limit for workers. And that's just to overcome the weight of the slab, not to mention the cabinets and everything in them. And you'd also have to assume that the friction coefficient between the floor and the legs would keep the thing from sliding before it tips (I find it more likely it will slide first, unless you have really rough floors and the leg bases are large).
Imo you would really need to work hard to tip this thing.
But I guess if someone decided to brace their feet on the opposite counter and push, and there was nothing in the cabinets, maybe they could do it.

Thanks for all replies. I’m still waiting to hear back from the cabinet and stone people to see what they have to say.

Going with a different top like butcher block is an option. I really want to avoid bolting anytiing down. I dont want to mess with the floors or electrical. I prefer the look of legs to islands with cabinets that go to the floor. And because of the layout of the kitchen and laundry room it would be nice to have the option to occasionally move the island over a bit to for example get large appliances in and out.

We are definitely keeping it bar height. Yes, we are unusually tall :) My husband and primary cook is 6’5” and desperately wants at least some surface in the kitchen that doesn’t kill his back.

Each side has one pull out drawer at the top for small stuff, but then the big cabinets for the heavier stuff do not have pull out shelves.

I think the fist drawing might be throwing some people off, so I posted another view. Some of those numbers are the dimensions of the recessed panels, not the entire side. The cabinet side is 17in deep + 1in overhang for top and the bar setting side is 11in deep + 1in overhang for top but it is it cantilevered. The legs are in the 4 corners. It’s the same dimensions as the current island just taller.

We also don’t and won’t be having kids, so it doesn’t need to be kid proof. We have all kinds of sharp corners, and glass, and unlocked cabnits full of poisen :) Just want it to be basically sound for normal adult use.

If you go with something other than stone it will become more of a tip hazard. The weight of the piece is what makes it resistant to tipping, so if you remove weight it will take less force to tip it over. With quartz it would probably take someone actively trying to push it to tip it (and since you know that it could tip over if you load it up on one side....just don't do it). But with butcher block it would be more prone to tipping AND sliding.