Here is the comparison of 455kHz vs 800kHz...

The 455kHz will be brighter overall ...but fuzzier...
The 800kHz will be crisper close to the boat...but darker out to the edges of the screen..



I use 455kHz when I looking for new structure because I can notice structure in the image all the way to the edge of the screen..then I drop a waypoint on interesting structure...

Then I re-position the boat to scan closer to the structure using 800kHz to see the details of the structure...

Frequency choices are specialized tools...use each for what it does best...

Rickie