Recommended power level for 5 GHz (Belkin RT3200)

I noticed that leaving the transmit power to 'driver default' results in the max power for a given channel being used. I got to wondering what a sane value is.

I tested values of 27 dBm all the way down to settings that simple would not register on my phone (iPhone 13) which I placed on a tripod a few rooms away from the AP.

I ran iperf3 to test 3 streams uploading to the server for 30s. In summary, the speed measured didn't change despite reducing the power by >100x. Channel 149/80 Mhz width.

27 dBm (501 mW)	365 Mbit/s
22 dBm (158 mW)	341 Mbit/s
17 dBm (50 mW)	388 Mbit/s
12 dBm (15 mW)	348 Mbit/s
7 dBm (5 mW)	375 Mbit/s
6 dBm (3 mW)	no connection

Given these results, what advantage does running at a huge value like 501 mW offer? What is a sane value to use?

I believe that depends on each persons situation. Remember that even though a client can receive a signal doesn't mean its reply is strong enough to make it back. In other words, you might be able to blast a long distance from the router but the client may not be strong enough to return.