I dont have extensive deep water experience with the Garmin so cant comment.
But i did have a Lowrance HDS9 Gen 2 touch hooked up to a TM260 (1kw). Easily spotted individual fish at 500-600m. Managed a pretty successful 1200 odd hours mainly fishing between 150-600m with that set up...and did pretty well with it too Wink
I'm planning to go to commercial level setup on the next boat for some super deep and lower frequency pinging. Will watch with interest to see what comes out over the next year. Last time I did
some reasearch it seemed to be that a major limitation is transom mounted 'ducers dont go down to low enough frequencies. Hopefully that gets sorted.