What is the worst latency value for machine

Please tell me the what is the highest latency value that machine could work properly for machining stuff
With lowest hardware configuration without Mesa boards?

Taking a look at other threads I believe that Latency is relevant only for parallel connector boards. PCIe ethernet etc etc boards don't have to generate the Steps to drive the motors so Latency test is not a true measure of their performance.

There isn't really a hard rule that says this works and that doesn't, it is much more of a soft answer of it depends... (I know not the answer you were looking for.)

The latency requirement really can depend on a number of factors. If the machine has need of generating steps, or reading encoder pulses in software (such as when using a parallel port), then the limiting factor will be the needed accuracy of your minimum sampling period (Base-thread.)

If those aren't a factor for your machine (if those things are done in hardware outside of Linuxcnc), then things such as the maximum speed of the machine combined with the maximum acceptable error tolerance combine to determine what the acceptable maximum latency should be. For example if your machine is very slow and/or you don't need particularly great accuracy, you can probably get away with worse (higher) latency.

Conversely, if you have a very high performance machine with high accelerations and want the highest possible precision. Low latency and a faster than normal Servo-thread will be needed.