XO ethernet over copper (EoC) - MTU

["scoobydooxp" at 64systems.com (Scooby)]

We recently had an XO EoC install turned up and it seems to have an odd 
MTU. XO Support had no idea what I was talking about when I called to 
ask. Does anyone know what the proper MTU should be?

Thanks in advance,
Scooby