EchoMap 74sv and 73sv differences?

[KSPropbender]

I'm looking at upgrading graphs and am sold on the garmins based on the features available at my pricepoint, but I need someone to dumb it down for me. I'm looking at the 73dv for my bow but can't decide if I want to spend the extra coin for side view at the console. What are the differences between the 73sv and the 74sv models? I've been reading the specs online and cannot for the life of me figure out why the 74sv is $150 cheaper than the 73sv. Anyone have any ideas? Also, can I network these two units, (the echoMap 73dv and the 73sv) and to what capacity? Can I share waypoints between the two? Can I look at the transom transducer from the bow unit and vice versa? I was originally looking at the Lowrance elite 7s at the bow and console until I found out the two couldn't share information since they don't run Ethernet ports

[Defiant]

The 74SV uses the Garmin Blue chart maps and has a 50/200 Transducer . The 73SV has the Lake VU HD maps and has a 77/200 Transducer . They can be hooked together and share waypoint's with nmea 0183