I have a Helix 5 SI GPS on my trolling motor, and just recently bought a Helix 7 SI GPS for my console, just like you. I haven't mounted the transducer for the Helix 7 yet, but I plan to mount it above the bottom of the boat. As jmp says, 3-5 mph is as fast as you need to go when scanning w/ SI. Running on plane does you no good since you don't have time to see any fish or structure to mark it, and your transducer is up out of the way in case you happen to hit any obstacles. I learned a lot about side imaging and transducer mounting from watching Humminbird you tube.