The idea of 6 foot chop is common on the Great Lakes. And chop in my experience usually means having the bow in one wave and the stern in the next as they can come that closely together. It is indeed daunting to be in the DS or some such sized boat when conditions like this kick up, and they often do, quickly and with little warning.
Once off one of the Lake Erie islands my wife nearly called 911 because, as she observed from the dock, the children and I kept disapearing in troughs no more than 50 or 75 yards away and she swore we had sunk.
I'll be honest though--when that sort of thing kicks up, you are incredibly thankful for the outboard! Trying to figure standard sailing amid that battering is like, well, too much, too fast for my brain! The clunk of the centerboard makes you feel like the bottom is going to rip off any second.