Need to know WiFi speed i7/i7plus ...

See this article for the standard maximum speeds for the various Wifi standards: Wireless Standards: 802.11a, 802.11b/g/n and 802.11ac

You can presume that if it is supported on an Apple device, it meets the capabilities within the standard.

GB

Apple specs not give in detail that I need to know

Then look elsewhere. 802.11 is an industry standard designation. The iPhone 7 meets these standards.

https://en.wikipedia.org/wiki/IEEE_802.11

On this page you will find the answers to your questions.

i.e.: you asked = 802.11n 5 GHz maximum speed is ?

802.11n operates on both the 2.4 GHz and the 5 GHz bands. Support for 5 GHz bands is optional. It operates at a maximum net data rate from 54 Mbit/s to 600 Mbit/s.

Hi auikung. These speeds are strongly affected by the WiFi environment, and the actual router settings. So it's not a question that can be answered in general. Also, if you're transferring data from the internet, the download speed will be limited by the internet connection, and by general internet performance. If it's data from a local server, the server performance will likely be limiting.

see >> https://www.apple.com/ca/iphone-7/specs/

Apple publishes the standards their devices have access to. Actual speeds will vary with the router and network they are attached to.

Look up the "numbers" for 802.11a, b, g, n and ac for cross reference.