Recently upgraded to a Helix 10 Mega SI, as I suspected the large SI transducer does not perform well at high speed with 2D plus I don't really like having it that low in the water. I need the 2D Chirp as clear as possible as I mainly run the lake around 20 mph looking for schools of stripers. The Chirp feature is awesome as I can run it along with old technology 200khz flashers Ray Jefferson etc. with no cross talk. (Old technology works really well for locating schools at high speed) I am looking for guidance or anyone with experience at using the Helix at high speed with an additional transducer. I will be transom mounting the additional transducer because I only had one sweet spot inside my hull and it is occupied. Does anyone know if I will sacrifice any Chirp qualities with the high speed transducer? I see humminbird recommends the XNT 9 20T (83 200khz)and the MSIDB cable. But I saw another transducer 9 XNT 28T (455/200khz) I realize the beam is more narrow but that may help me. Would the 455/200khz help? Any experience or guidance on transducers or settings will be appreciated.