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if you have two (or more ) Tangnano, you can try it, you need the 'dev' branch and
2 free pins on each tangnano (RX / TX).
For short distance, you connect this pins direct (RX<->TX) or using RS485/RS422 converter for long distance.

Rod, he has huge excursions on both sides of the graph, those are not shown unless using --show, and those are the ones causing latency errors and link drop.

Look forward to seeing how that goes, Tang Nano's are about 30 bucks AUD, two of them are still cheaper than any FPGA with a similar total pincount. I'm being selfish but that also means I stick with the same FPGA hardware for every machine I can possibly imagine making. 

Let me know if I can help with testing, I'm currently retrofitting my three machines to closed loop to the controller, so there's room for some hardware experimentation. 

A broader opportunity could be to try and get involved in plant automation. This will get you using a lot of fieldbus technology like ethercat which is transferrable to CNC machines which are only a very small subset of this automation industry. 

Removing the Wifi board is probably good for latency.
The DKMS driver can usually be installed with 

sudo apt install r8168-dkms
but you do need to have non-free in the apt sources. This is included in the Linuxcnc ISO

Seems the card uses a R8168 interface. The R8168 requires a DKMS driver to get acceptable RT  performance. Not sure how that goes with a Pi. I would not use it for ethercat but would be fine for general network use.

Sometimes the shape is because of the number of sbins samples. You have 20 mand most use 1000

try
latency-histogram --nobase --sbins 1000

My observation is that Ethercat is faster than Mesa hm2eth. 90 usec will be fine If your pings are good

Problem with "Joint 0 Tracking Error" and Real-Time Delay: Resolver-Based System

System:

LinuxCNC with PID control

Resolver-based feedback (no encoders)

3-axis machine (X, Y, Z)

The HAL/INI structure includes: Ibarmia core servo.hal, Ibarmia MotencMotion.hal, motenc.ini, etc.

Main Problem:

When attempting to move any axis (especially the X axis), I immediately receive the following critical errors:

Joint 0 Tracking Error

The axis does not move, and the error appears as soon as I attempt to move it, regardless of the velocity or acceleration settings.

Measures already taken:

Latency Test

Maximum jitter on the base thread: around 16,600 ns

Increased the BASE_PERIOD value from 50,000 to 100,000 to reduce RTAPI errors.

INI Tweaks

Reduced the MAX SPEED and MAX ACCELERATION values ​​on [TRAJ] and [AXIS_0] to very conservative values:
MAX SPEED = 5.0
MAX ACCELERATION = 300.0
FERROR = 100
MINIMUM FERROR = 10

It appears to boot, but after 10 seconds, it fails.

Try 2.4 GHz. 5 GHz is not as reliable in an industrial setting and has much shorter range. I turned off all my 5G wifi

Failing that use a wifi USB dongle that has an external antenna and get a SMA bulkhead mount cable to extend it outside of the cabinet