In my experience, it makes a large difference in network latency
to use isolcpus and pin the Ethernet device IRQ to the same CPU that's
running LinuxCNC's realtime.
For example, I'm typing this on a HP 800 G1 Elite that I use for normal
browsing, compilations, videos etc. At the same time, it is always running
LinuxCNC. Without IRQ pinning, it would drop (timeout) a packet maybe
once or twice a week. With IRQ pinning, it never drops packets...