Poor wifi performance

Hi, on my first floor I have a EX 6120, used as an access point. Its connected with a cat6 Network cable to a switch in the basement. My Internet is 1000Mbps, up- and download. If I test my speed on my PC I get almost 1000Mbps. When im connected over the EX6120 I never get more than 60Mbps. I tried changing channels, speed still low. I have both networks enabled, 2.4GHz  and 5GHz, both has the same SSID, so that should be all right. No matter if I test with a mobile or a Notebook, the speed is always same low. 

In the first floor i have a Nighthawk X4 AC2200 also connected as an acess point. there the performance is a bit better but i never get more than 300Mbps. I use different SSID there, also connected with a cable to the switch in the basement.

What can I do to get higher speed? Should i use different hardware as access points of my network? Are the range extenders not a good solution to use them as access points? Thanks for any help, advice.