I own both but I/m selling the 1290 - As you know from the reviews the 1290 is a "beast" - Its a magnificent bike. Smooth, well built, everything works etc.
However, unless you ride your bike on open roads with large high speed sweepers its a waste. The 790 isn't as fast of course but the handling is superior for tight twisties and every day riding. The 790 is lighter, smaller and just a big more user friendly in real world riding. Thats not intended to take anything away from the 1290.
I need to add that I'm and old guy (80) and not a big guy either - I rode my 1290 over 12K miles and enjoyed it but in the first 5 months I owned the 790 I put 8000 miles on it and thoroughly have enjoyed.