Monitor for new gaming PC?

Hey guys, hoping you can help me. I just build a new PC for gaming. It has an i7-6700k and a GTX 1070 and so I know it’s capable of playing games at higher resolutions. But I’m wondering if I should go 4K, or with a 1440p high refresh monitor.

These guides rank the ASUS ROG SWIFT PG279Q 27″ as highly rated:

https://elitegamingcomputers.com/best-gaming-monitors/
http://pc4u.org/best-gaming-monitor/

But if I’m not playing competitive games, does the refresh rate really matter that much? Can I get away with a 4K monitor with a 60Hz refresh rate?