I would guess that since you ride singletrack on a KTM your focus on dualsporting will be similar to mine. On the trail is where you will have the most fun, and that's where you'll spend most of your time. IMO, the smaller the bike, the more you would enjoy it. A 690 Adventure should certainly be a strong consideration..................... once it becomes reality.
The F650 GS twin is a street bike with long travel suspension, which is exactly what I want. The 800GS will take you a lot of places but you'll have to work at it, and pay for it, and wait for it. It's almost 400 lbs dry. I do a lot of offroading on my DR650, and although it's 60 lbs lighter than the BMW, it's still a pig.
BTW, I started riding dirtbikes in '92 and just sold my last race bike, a '04 KTM 300. I started dualsporting 2 years ago, and I'm loving it! But I want some variety like you do. So to replace my SV650, I ordered a new F650GS twin. When I need to get muddy, I'll hop on the DR650 and not worry so much about dropping it.