1. Chris, I think you may find the MBS Atom wheels are narrower than your longboard skateboard wheels. That could give you less rolling resistance and higher speeds. Conversely the softness of the MBS tires might take away enough of the narrowness advantage. One thing I know about that comparison is the MBS wheel diameter will just roll over some pebbles that would stop your longboard skateboard wheels. That is most important when you are doing a slow jibe and the sail blocks enough of your vision that you can't see the pebbles you are turning toward which are large enough to stop wide skateboard wheels. That reason is why my first longboard skateboard was sold to me by a guy buying a mountain board. And it is the reason why my own experience land sailing that longboard led me to buy mountain boards.
2. Answering your questions, Chris. I don't currently use any of the wide longboard skateboard wheels, even though two of my land sailing boards have skateboard trucks. I put 100 mm diameter, 22 mm wide scooter wheels on my 59" deck Kahuna Creations Bombora; the original 70 mm diameter, 58 mm wide Kahuna wheels were used only 2-3 times before I made the change. To make my 57" deck Turf DeVille mountain board useful I took off straps, brakes, trucks, wheels, tires I put on skateboard trucks with 125 mm diamter, 22 mm wide scooter wheels, and had to make cutouts for the wheels because the skateboard trucks were much shorter than the vastly over-weight, over engineered, independent suspension, original trucks. I had purchased Exkate 80 mm diameter, 50 mm wide longboard skateboard wheels for the Turf DeVille , but used them only about 5 times before I purchased the scooter wheels. Scooter wheels have the same axle diameter openings as longboard skateboards and inline skates.
3. On two land sailing boards I still use their original inflatable wheels and mountain board width trucks: an MBS Blade, 8.5 inches diameter (235 mm), 40 inch deck, 50 inches overall length, 10.5 inches width at the widest point; and a Carveboard with their old style wheels (inflatable from 10 to 50 PSI), 7.5 inches diameter (about 190 mm), 43 inch deck, 50 inches overall length, 11.5 inch deck width at the widest point. The Carveboard was designed for going down streets & sliding around curves, so it did not have brakes or foot straps. I'm just now thinking mountainboard wheels might have the same axle diameter openings as the Carveboard and if so, would produce less rolling resistance because they are narrower than the Carveboard wheels.
4. I also have a 79" long Speedsail board with 12" diameter tires (designed in France by Baron de Rosnay around 1976 for sailing on hard sand beaches). I hardly ever use it because the deck is only 9" wide. Compared with my other boards that is not wide enough for comfortable foot movements while jibing. Also the wheel diameter puts the deck higher above the ground than I like. I believe it's length was designed that way too handle the very long boomed, pin-head sails used then.
5. My successful land sailing so far has only been on parking lots & very rarely on streets. I've briefly tried grass less than 5 times; too bumpy & too difficult to get going.