The Garmin product set is pretty straightforward.
4000 - keypad
5000 - touch
6000 - keypad with new faster processor
7000 - touch with new faster processor
I thought the touch was a gimick until I tried using it. Picked Garmin (5000 series) over Furuno
mostly because I find the touch more intuitive. You drag the chart around on the screen to pan instead of using buttons. Sort of Iphone
vs. Blackberry. Really personal preference. I find the speed of the 4000/5000 to be fine (especially after a software
update in the fall). Much faster than my previous 2003 era Raymarine
but I assume new Raymarine's are faster too. The newest Garmin models are really fast. Not sure I'd be willing to pay the extra money
for the speed.
I really find the larger amount of chart you can see on a 12 inch screen worth the extra money
All of these Garmins support NMEA 0183
, NMEA 2000
and Garmin's ethernet. You can (and I do) use all three at once. I've found the Garmin's to be better than average at compatibility with different inputs.
Really, all of the chartplotters are so much better than five years ago that you are likely to be happy with whatever you get.