Hi Kevin,
I have used pretty much every Garmin portable since 1993, and the Aera 660 and the larger Aera 760 are by far my favorites.
The Aera 760 is quite a bit thinner (0.9" versus 1.5") and lighter (19.8 oz versus 26.4 oz) than the Aera 796.
The Aera 660/760 also have a WiFi interface which the Aera 796 doesn't have. This wireless interface can be used for downloading software and databases, and for receiving free weather from FlyGarmin to show NEXRAD and graphical/textual METARS for your planned route of flight when doing flight planning at home. The WiFi weather also populates the weather related fields on the Aera 760 like temperature, wind speed/direction, and baro pressure. I run an Aera 660/760 24/7 in my house to display temperature and NEXRAD weather and provide a quick check of the METARS for any of the area airports before I go flying.
The Aera 660 and Aera 760 can do something that no other portable or tablet in the world can do, which is listen to the MapMX RS-232 output from a Garmin navigator and display an accurate curved flight path for routes, SIDs, STARs, instrument approaches, and missed approaches - just as they are shown on the IFR navigator. These curved path depictions even include dynamically adjusted procedure turns and holding patterns as shown on the navigator.
The Aera 760 can also display MapMX overlaid over an approach chart integrated into the moving map. This is something that not even the Aera 660 can do.
I don't use this feature since I have a GNX 375 driving the Aera 760 in my plane, but if you don't have a compatible IFR navigator and want to create flight plans, including departures, arrivals, and approaches, and even airways, the Aera 760 will let you create these. This is something else you cannot do on an Aera 796.
One of the big pluses for the Aera 760 is that its snap-in mount uses a 9 pin D-Sub connector that saves cost if you want to make installation specific wiring harnesses and use the Aera 760 in multiple planes, cars, homes. As you know, with the Aera 795, you have to buy a bare wire mount for each place you want to use it if you wire it into the plane.
You can make your own wiring harnesses to plug into the Aera 760 mount, or buy these bare wire harnesses from Garmin and install in each place where you want to provide power and data to the Aera 760.
I am probably leaving out some key differences, but I would encourage you to visit the
Aera 760 web page and since you are so familiar with the Aera 796, I am sure you will readily recognize the many differences.
Steve