Measure data transfer rate (bandwidth) between 2 apps across network using C++, how to get unbiased and accurate result?

I am trying to measure IO data transfer rate (bandwidth) between 2 simulation applications (written in C++). I created a very simple perfclient and perfserver program just to verify that my approach in calculating the network bandwidth is correct before implementing this calculation approach in the real applications. So in this case, I need to do it programatically (NOT using Iperf).

I tried to run my perfclient and perfserver program on various domain (localhost, computer connected to ethernet,and computer connected to wireless connection). However I always get about the similar bandwidth on each of these different hosts, around 1900 Mbps (tested using data size of 1472 bytes). Is this a reasonable result, or can I get a better and more accurate bandwidth?

Should I use 1472 (which is the ethernet MTU, not including header) as the maximum data size for each send() and recv(), and why/why not? I also tried using different data size, and here are the average bandwidth that I get (tested using ethernet connection), which did not make sense to me because the number exceeded 1Gbps and reached something like 28 Gbps.

SIZE    BANDWIDTH
 1KB     1396 Mbps
 2KB     2689 Mbps
 4KB     5044 Mbps
 8KB     9146 Mbps
 16KB    16815 Mbps
 32KB    22486 Mbps
 64KB    28560 Mbps
 

HERE is my current approach:

The perfclient code can be accessible here: https://github.com/bobdanani/Performance-Bandwidth-Test-Client-Server/blob/master/perfclient.cpp

The perfserver code can be accesible here: https://github.com/bobdanani/Performance-Bandwidth-Test-Client-Server/blob/master/perfserver.cpp

Is there anything wrong with my approach? How can I make sure that my result is not biased? Once I get this right, I will need to test this approach in my original application (not this simple testing application), and I want to put this performance testing result in a scientific paper.
If you try to run my codes on your machine, let me know the result that you get (at least for 1024 bytes, 1472 bytes, and 64KB data size), and let me know what internet connection types you are using.

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