Nobody asked me but I'm going to kick in my 2 cents. I have had a Fishmark 320 on my console for about a month now. (Del installed a 320 on his TM a week ago and loves it) It is a great improvement over the X-75 I had there. I have not seen a Fishmark 480 in person. The screen dimensions of the 320 and 480 are identical. Both are 3.5" X 3.5". There are 50% more pixels/inch on the 480 than on the 320. The 480 has 136 px/inch. The 320 has 90.7 px/inch. Does this make a great deal of difference in sharpness and clarity? I did an example web page to represent the two screen displays. I made two identical figures, one @ 90.7 px/inch for the 320 and the other @ 136 px/inch for the 480. Take a look:
Certainly the 480 appears crisper and less jagged than the 320 at normal computer monitor viewing distance of 12 to 24 inches. But are you that close to a graph on your boat? Take another look at the page, but slide your chair back until you're 4 or 5 feet away. Still see a marked difference? If so then the 480 is for you. Personally, I can't see much if any difference from 4 or 5 feet away. But then that's MY eyes!
Other things to consider besides clarity are reliability and performance. The 480 X 480 screen is new and although I'm sure Eagle has tested it thoroughly, the components have to be smaller, and the connections have to be smaller and more numerous, Have these been tested in the bow of a bass boat crashing through 5 foot waves on Pleasant or Roosevelt lakes? Not yet. In comparison I haven't heard of any problems with the 320 X 320 screen in the last year.
The other thing to consider is performance. I can only speculate that if Eagle did not increase processor speed to handle the larger amount of data going to the 480's screen (twice the amount of data than the 320) then scrolling speed or refresh speed would suffer. That's really speculation too and the only way to tell would be a side by side on-the-water comparison.
Am I kicking myself for buying a 320 @$170 instead of waiting a month and getting a 480 @ $209?? Absolutely not. Keep in mind I am not an "early adopter". I waited a few years for the X-15 technology and software to sort itself out before buying a discounted, clearance priced X-16CI. Then I waited a year for the 320 and got that at a discounted price.
The 320 is still a great graph and a great value for the money. If you need to own the latest and greatest then buy a 480. JMO