I checked again last night on my 478, as I am heading to the keys next month. I saved my tracks from the last 2 years, and they are still there even though the active memory is at 100% used, kinda like they have a reserve memory for saving tracks. I would be surprised if the newer more expensive models do not have this ability also.

West Marine has a Garmin 546s plotter/sounder for $840 with a $200 rebate and the transducer and flush mounting kit is around a $100, so the whole set-up after the rebate will be $750, I think for that model that's a great price, thoughts.