If the Helix 9 is the G1, it comes with the compact SI transducer. If upgraded to the HDSI transducer the images would be similar to the 997.
If upgrading, I would go all the way to the Helix 9 CHIRP MEGA SI.... The 10 would be even better. You get the mega frequencies, chirps sonar and imaging and a dedicated DI element in the transducer. This would be a major step forward from your 997 while the g1 unit would only give you a faster processor and a brighter display and maybe better pixel density.