4k Monitors - Suggestions

Just wondering how many people are using 4k Monitors in a production environment?

**-**How has your experience been with them? (specifically with corona/mac/Photoshop)
**-**What model/Make are you using?
**-**Are any recommendations on upgrading a few offices?

One of the main considerations is to have Color Correct Calibration - We will be using this across two offices and want the artists to be seeing & working on the same visual color correct image.

Thanks for any help. All the best.