5G is a new Cellular system rolling out. It's speed depends on the same things your phone's cellular system depends on.
5GHz on WiFi can be called Dual Band since most of these can supply 2.4GHz links as well.
Test on a 2.4GHz link and for 5GHz I find I can't be as far away as my 2.4GHz links. Figure 20 feet to router when testing.
I have Netgear modem/router. Great speed coming from Comcast proven with other items connected wirelessly. Problem exists in my desktop which only has 2.4 so added a Netgear 5G adaptor. If I go directly to from computer to router for speedtest it produces 170Mbps. BUT, through browser (Chrome, Firefox, Edge) I can't get more than 13Mbps.