Wow! Was I wrong. I frankly don't care what the spec sheet says. The 3590LMT is huge compared to the 3490LMT and I like it 100% better for that reason only. I found myself having to really focus on reading text on the 3490LMT especially on things like photoReal junction imagery. Those concerns are gone with the 3590LMT.
Here are some comparison pictures between the two devices:
The difference in the screen experience in this photo is real. The 3490LMT is brighter, but the colors are more washed out. The colors on the 3590LMT are more rich and deeper. I much prefer the 3590LMT screen after having both devices side by side.
Something is up with the routing on these two devices. I have the exact same route calculated on both devices. The two devices agree 100% on the route to take. They agree on the miles. But the 3590 has me arriving over 2 hours earlier than the 3490 on this 22 hour trip. I've never driven it so I don't know which is more accurate. Also note that the 3590 is 2 hours quicker WITH a red traffic icon, showing a 15 minute delay leaving Las Vegas. The 3590 is getting a traffic signal through Smartphone Link. The 3490 does not have a traffic source.
I wonder, since the 3490 has no traffic source in the photo above, if because of that it doesn't take historical traffic data into account? Perhaps that feature only works when there is a traffic source connected?
The only other difference between the two units is that the 3590 has a firmware v4.70 upgrade available for download out of the box. The 3490 reports the latest available as v4.40. Not sure if the firmware update has any impact on routing calculation or not.
There is no difference in glare on the two device screens. The apparent glare on the photo above is strictly a limitation of the environment that I took the photo in.
There is a thickness difference as well between the two devices as can be seen here.
I was somewhat disappointed to see that, out of the box this brand new unit had two-version-old 2012.2 maps installed. I had to do a map update out of the box to get to 2012.4. Not sure why a brand new device that just shipped two days again would have 6 month old map data on it. I could see having 2012.3. Perhaps I simply don't understand the production cycle on devices like this.
Finally, note that currently the 3590LMT has the same problem of an incompatibility between Smartphone Link Live Traffic and the HD Radio traffic described in my earlier blog posts. No update from Garmin as of yet to fix this problem.