Q: 1440p external display with a MacBook 12inch (2015 or 2016)

Hi everyone!

"Dual display and video mirroring: simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels at 30Hz on an external display, both at millions of colors"

Does anybody use a 1440p (2580x1440) external display with a MacBook 12inch (2015 or the new 2016 model)? Are there still 30Hz or are 60Hz possible? Can anyone share his experience, thanks? :-)

Best regards from Germany,
Marvin