I used to work for Cabelas in the product information department and the main problem people had with seeing fish deep down is their cone angle of the transducer. It wasn’t so much the resolution because anymore the higher ones are at least a 480X480 resolution. If you have too large an angle you aren’t going to see down deep in as much detail as you would if you have a smaller cone angle. The newer ones have almost completely gotten rid of that worry because they are either dual or triple cone angle built in.
Lowrance definitely has some good techs if you speak to the right person. I have been on the phone with them several times. Their website has a huge amount of information on it as well. Hope this helps.