Yep the screen is better and more responsive but the biggest difference for me with the XT vs 590/595 is the software and connectivity.
If your creating complex routes like me then the XT has some big advantages in this area.
590/595
For complex routes you end up using Garmin Basecamp software.
This has to be installed on a Windows or Mac PC/laptop, and to transfer any route to your GPS you have to connect it with a cable to the laptop. This means I normally have to take my laptop with me to do updates when doing a trip that may change or when the iron butt event I'm doing doesn't disclose the checkpoints until a couple of hours before the start.
Basecamp is comprehensive but complex and fiddly when compared to google maps etc. It feels like it was designed in the 1990's.
XT
This connects to your wireless network and will receive software/map updates automatically when turned on. It gets new/modified routes in the same way. If your wireless network covers your garage you can leave the GPS on your Spyder and just switch it on to receive any changes. It also helps that the battery on the XT actually works, unlike the 590
To plan routes you use Garmin Explore. From a PC, Laptop, phone or tablet you can access the Garmin Explore web site and plan routes there. There are also dedicated Garmin Explore Apps for apple and android tablets and phones. This means when I'm travelling just having my phone is enough to create and update routes.
Garmin Explore doesn't have some of the fancy stuff of Basecamp, but its faster, easier and the syncing is automatic. There's still a learning curve to get the best out of it but not as much as Basecamp. The maps themselves are nicer with proper topographical, google and satellite options.
Routing and GPX points
If you've not used software to plan routes on GPS devices before, one thing to be aware of is that when Basecamp, Explore, etc send the route to your device they are only copying the points you've specified not the roads themselves. The GPS device it recalculates the route from those points based on the preferences setup in that device.
If there is a choice of roads and you want to use a particular one its worth putting one or more on these roads to force the GPS to use the right ones. For example I have dirt roads setup as avoid on my device as I don't want it sending me off down them at random - we have a lot of dirt roads in NZ
However sometimes if you don't use them you'll end up doing a big detour, so for the instances I'll add a couple of extra points along the dirt road to force the GPS to use it.
