According to Musk, 0.5 mach max speed.
He also said it can corner better than any car in the world due to massive downforce. And that it'll be in production in 2028.
We'll see.
I don’t trust a word that guy says.
https://mcmurtry.com/upside-down-driving/
McMurtry says the hard part isn't the suction, really, it's making the skirt work across a variety of road conditions, so you don't lose cornering ability when you need it most. That track Tesla built was very smooth. It's possible they can do what they showed, and not be able to do the same on a regular road.
Tesla is an unserious car company, led (for some reason) by a person who supports 1) the destruction of incentives to buy EVs, and 2) the destruction of the climate more generally. I hope the people putting money down on this farce lose it all.