I do not know much about the Hummingbird product, but I just bought the Lowrance HDS7 and HDS8 units along with the downscan. Wow! It is awesome. I would recommend you get the largest screen size you can afford. Check out either of these two places. They are great people and will answer any questions you might have: bbgmarine.com (this is where I got mine) and threeriversmarine.net. I do not think you will be disappointed. Check out the BBC forum and you can do some research on the two brands and see some of the screen shots.

Good luck!