What is your preferred price range? Your X135 does not have GPS, how does it keep you in the lake/river channel? With the tranducer on the transom, by the time you are too shallow its too late. I have the HB 788Ci with Navionics Premium map card and I am using a QuadraBeam transducer (poor man's side imaging). The GPS Map detail is outstanding, the unit has 640x640 pixel resolution, and the sonar features are great. I think you would find color is also a significant benefit as compared to gray scale. The 788 unit is now available with Down Imaging. Go to
http://www.bbgmarine.com/ for the best pricing and service. Also if you want to do more research, go to
www.bassboatcentral.com aqnd look at the Humminbird and Lowrance forums.