I realize that the 858c HD is the latest unit, but what are the main differences between the two? I would assume that the HD unit has a much faster processor and probably has a much crisper sonar display.
The reason I ask is I can get the 858c for a lot cheaper than the 858c HD unit and the 858c is also ethernet compatible, which means that I would be able to use the unit paired with the iLink once I decide to upgrade to that down the road.