My Apple iPhone 6 and MBP’s can all connect to my wifi router (which has 2.4GHz and 5GHz broadcasting as the same name) quickly and get the full 300/100 on speedtest.net

My windows devices seem more fickle, and more prone to connect at 2.4GHz.

Windows 10

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Click on wifi icon, then press properties.

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Useful status. Notice here it is connecting at 5GHz

If I get close to the router broadcasting on 2.4 and 5GHz, I can connect at 5GHz.

WiFi

From the SO Question

| Gen     | Standard | Band            |
| ------- | -------- | --------------- |
| Wi-Fi 1 | 802.11b  | 2.4 GHz         |
| Wi-Fi 2 | 802.11a  | 5 GHz           |
| Wi-Fi 3 | 802.11g  | 2.4 GHz         |
| Wi-Fi 4 | 802.11n  | 2.4 GHz / 5 GHz |
| Wi-Fi 5 | 802.11ac | 5 GHz           |
| Wi-Fi 6 | 802.11ax | 5 GHz           |

Sometimes it seems better to force a certain band:

5GHz only:

  1. Device Manager » The wireless card » Properties » Advanced Tab
  2. 802.11 a/b/g/n Wireless Mode set to 1.5GHz 8021.11a
  3. 802.11n/ac Wireless Mode set to 802.11ac

2.4GHz only:

  1. 801.11 a/b/g/n to b/g only (and not dual band)

Mac

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The Mac can connect to the SSID on 5GHz.

Option and click on the WiFi symbol to get these diagnostics