I have just got a U2720Q, it worked at 60Hz right away. But I am connecting over USB-C, with the provided cable.
What it did find off-putting is that Dell say they don't test with Macs, and thus can't support them, but they just assume that Appl follow the same specification they do. A bit weak, but the monitor does work fine.
I ended up going with Dell U2720Qs, and after some tedious initial work to get them running natively at 60hz, they're fine.
I would have bought the Apple displays in a second though if they had been priced up to maybe even 3k each.