.

Need a little help here. I'm getting ready to
make a (big for me) upgrade to the sonar on
my boat. I've been using a FishMark 320 and
want to get a side imaging/down imaging sonar.
I want the big screen.

What is the difference between these two units ?
From some descriptions on the internet they seem
to do the same thing, but one is $500 more than
the other. I'm sure I'm not reading everything
right.


thanks, Chris