The Ethernet SS seems to be very robust regards noise, I have heard of it being tested sitting on top of a plasma torch and it not falling over.
I never really suffered any noise issues with the USB version anyway, did have a slight issue on one machine where if I hit the E-Stop (dropped out all contactors) it would occasionally crash the SS but that was solved by removing the cap and resistor on the SS.
I have the ESS on the big lathe and it is nice, still one niggle for me with the SS and that is Step/Dir spindle is not 100%, it seems very occasionally it will skip a beat, its for a very short duration and doesnt trip the drive but you can hear it. Also if varying the spindle speed via the Override Pot it clunks a bit. Greg knows about this and has done for at least 2 years but so far nothing has been done, probably because there are very few that use servo spindles via step/dir so it wont be high priority.
Regards backlash comp, that has been dealt with, probably getting on for a year or so, and it works well by all accounts..
Hood