[kayodelycaon]

They don't have HDMI port, so you're limited to your adapter or the TV's display port capabilities.

[bombcar]

If you're dependent on the adapter, you need to use the Apple ones, or you need to have multiple. Sometimes HDMI works, sometimes it doesn't, changing the adapter usually fixes it.

[microtonal]

Sure, but there are plenty of adapters that drive 4k@60Hz without an issue, such as the latest revision Apple's adapter (old revisions would only do 4k@30).