On most any of the newer sonar units you can expand the bottom detail or zoom etc.
There will be a lot of fish you will never "see" that are holding tight to structure or hugging the bottom.
If money is not an object I would suggest you look into the side-imaging units 797c2 or 997c2 by Humminbird. Get the upgraded version with the maps on it for only $200.00 more. Well worth the extra costs.
The side-imaging will open up a whole new underwater world for you. They'll all have this technology soon enough but right now Humminbird has the patent.
Trust me, it's COOL!