J
I say leave it out. I'm a bit of a "llama" as you put it. But I have managed to learn from not knowing pretty much anything to knowing how to setup a network with pfsense doing my routing, with port forwarding/NAT etc, and I know what almost all the options do etc.
Just by reading everything and asking the odd question, infact I chose pfense because it looked like the easiest one ( I think I was a little wrong on that call though :) ).
I remember one of my questions being, "why is my red/WAN nic running in halfduplex mode, is it supposed to be?". I guarentee if that option were avialable I would have definatly tried it before asking any questions or reading up on what it did, until I broke something.
But in saying that, all it needs is a little warning beside it such as. "Leave this to auto unless you really know what you are doing, as it may lead to a duplex mismatch which will degrade performance".