Marking at speed will depend a lot on your hull. I had a Garmin 741 on the boat that was losing power. It wasn't the wiring and I could never mark fish at speed with that unit so I upgraded to a Raymarine that had the 3D scanning thing. Thought that would be useful for trolling, but it wasn't as life changing as I had hoped. Anyway, with the Raymarine I have essentially a 2023 vintage transducer and I still can't mark fish at speed. I have a Key West with a stepped hull and it just throws off to much turbulance for a transom mounted transducer. Not sure if going to a thru hull would help, but just be aware that hull design will affect you ability to do that.