I had a 950 before switching to the F800GS.
The 950 motor is more exponential.....so, quicker on pavement but more challenging to control in the dirt. The F800 is much smoother and more linear power band. You need better throttle control habits for the 950/990 offroad.
The KTM stock suspension is better. After $2k upgrade (
) my F8 performs admirably.....once brought up to my personal standards.
My 950 averaged 35 mpg fuel consumption. The F8 is getting 50+ mpg. Not sure how the 990 compares.
The maintenance routine on the 950 was a real PITA......ridiculously so. And I'm a good mechanic that likes wrenching. I got sick of working on my 950. Too much crapola to remove for simple tasks like oil change. They say you get used to it. I never did. Probably biggest reason I sold it. Bike was a real hoot to ride, otherwise. Well that....and I had to pick it up once.
Ho-chi-momma that thing was top heavy tough to stand back up for this 5' 9" old fart.
Comparatively, the F8 is a breeze to work on. It's well thought out for easy access with good fit & finish. Haven't had to do much to it anyway. I like this aspect much better. AND its quite easy to pick up! I think that's due to the lower and better mass centralization primarily due to fuel location.
Both are super fun bikes with their own quirks......and expensive to own. I had a lot of fun on my 950, but have definitely enjoyed my F800 more.
Ps. Seats are very easy to modify or replace to your liking.....not a serious factor.