Exactly the same Q I posted a couple of months ago, the answer I got was no difference apart from screen size, I can second that now.
BTW I think overall I liked my old 8 years young lowrance better, screen was bigger definition was less though (I bought the 4100) I find myself taking my polaroids off to view it never needed to with the L + other things I probably need time to settle into the 4100 and get it's entire setup spot on.
cheers fnq