Nice instrument the Garmin. Is the depth reading you are referring to the depth on the chartplotter map or is there a link to a seperate transducer. For depth you need a seperate transducer to take the reading so therefore a seprate display usually. Not sure if the new chartplotters show all the readings. If Garmin had been as good as it is now when I bought my C80 I would have proabbly bought it, but oit was not comparable 5 years ago IMHO.
Depth is important as you can read it and correspond to a map so for me it is the number one or first device. We have the Raymarine ST60 series depth, wind and speed log, autopilot seatalked into a Raymarine C-80chartplotter. Bet you could pick them up used.