Getting rid of the buzz generally means twin cylinder. You said you're on the highway a lot, so that further reinforces moving that direction in my mind. The parallel twin BMWs are okay bikes, but they have some quality issues and while capable, really are not any more enthusiastic in their operation than your current bike. Group I ride with used to be mostly F800GSs, and there's not a single one left. ECM failues were the number one issue, followed by boring riding experience, poor suspension geometry for soft off road stuff, fuel system failures, and electrical issues. For a while, literally every trip we went on had a failed BMW issue.
the group now runs the gamut. Tenere 700, KTM 790 and 890, an africa twin, a new Desert X, a Triumph tiger 800, a 1200GS, a 1090R, and me on my 990. The 790s have had dust ingress issues, with two getting new warrantied engines. The others have generally been reliable. All except the KTMs seem to have very brittle plastics, constantly breaking things when dropped.
Most adventure bikes have soggy suspension stock. This is true to varying degrees for all of the above except the 790 and 890, and sort of the 1090R. Everyone except the 790 and 890 riders have done at least spring upgrades to remedy that, fortunately most bikes have reasonable bones to work from to get passable adventure and street performance, so I'm not sure I'd worry too much about that. The KTMs really are a step up if you're going to get aggressive, a lot of the fork architecture is shared with the dirt bikes.
Tenere 700 power is very soft, but it sounds good and feels willing enough. Africa twin has a little more off the bottom by virtue of displacement. Both are dramatically stronger than a single cylinder F650. All of the other bikes on that list have quite a bit more zip, which is nice on the highway. the Triumph triple sounds really good but you have to rev it to get to the juice. Fortunately it's happy enough doing that. The KTMs are the most agreesive feeling (ready to race! lol) and the BMWs are the most rubbery. At the end of the day, every single bike on that list has more power than most people use on an adventure bike off road if you let them rev.
I owned a 790 for a bit, it was a good bike once the intake was fixed and a few other key parts replaced. I sold it because the 990 is a better bike for what I do.
The big BMWs are an interesting riding experience with the telelever front end. I find them to be great pavement-focused bikes with the best weather protection of the bunch, but not confidence inspiring off the pavement with the rake changing all the time.
Weather protection from the others on the highway are all a step down from the big BMW, but roughly equal. My 990 is definitely the worst of the bunch in this regard. 990 gas mileage is also horrible.
The seating position on the Tenere 700 was also very awkwardly far back for riding in loose stuff seated. It's fine standing up though.
Generally, a lighter bike is always better. Tenere and 790/890 win there. My 990 is the lightest of our group, but it's got a lot of holes drilled in it.
So there's a whole bunch of opinions that may or may not help. I usually recommend the Tenere 700, or the 790/890 if a person is wanting more aggression and is okay working on stuff. They are light, capable, have "enough" power for most people, good parts and aftermarket availability, and enthusiastic supportive owner groups. While I've been around the Tuareg and Desert X, I don't know enough about them to recommend them yet.
And for me, the 990 is always going to be my favorite. I've had 4, put well over 100k miles on them, and it makes me giggle like a child every time I ride it.
Though I did just buy a 690 to build a rally replica out of. Time will tell where it fits into things, so far it's a good dual sport bike with an awkward transmission that prevents me from recommending it for highway use. The suspension keeps it from being a race bike, but because KTM, that's an easy enough issue to fix. It's plenty good for adventure bike use though.
