I believe 240 Hz is the highest,
However, the game engines are limiting monitors. 240 Hz won't be supported anytime soon I don't think, except perhaps really competetive games, because the gaming market is the market that's the easiest to brainwash.
As for as overclocking is concerned, that's luck, because some overclock better than others. And some are built so that they can't be overclocked with weaker components. They're dirt cheap to produce, yet they take huge prices on monitors. Thank e-sports for that.
I believe there's no a MSRP for the ASUS monitor, but rather to just show off that they can do it. Maybe we see prices later on, if they decide to manufacture it, but I doubt that. If they released it, then they wouldn't make as...