OK not exactly what you asked, but I've ridden an F800GS and a KTM 990 adventure back to back on the same day. Both completely stock dealer test bikes.
The KTM is quicker, it's got a ridiculous amount of shove to it, very torquey and a completely different animal to the 800. It's a bit better at handling motorway cruising thanks to its fairly low gearing, and it's got a much better screen (Though you say you've changed yours anyway).
The 800 is more of a fun bike, less serious than the KTM if that makes any sense. they're both great down little gravelly back roads, but thanks to the weight the 800 just feels more at home there to me (though I'm no offroad god, never even seen proper dirt!). Also I found there was more feel in the suspension than on the KTM, which felt a really tiny bit like the 12gs in that it was beautifully stable but you don't get quite the feel from the wheels, it just plows through bumps without a care in the world. In terms of handling I thought they were really very similar to be honest, both have massive front wheels and masses of ground clearance, and both good fun.
The 990's fuel delivery is really jerky, the 800's much smoother in traffic, but then you asked about the carb fed 950 which I've heard is as smooth as you like.
Personally I fell in love with the little 800, I think it's a great bike. The KTM's just as good, perhaps better, though it's more of a serious bike, it's a bit of an animal. It's got more grunt and is a more practical tourer, but the lightness of the 800 means it's more fun down less travelled roads.
I'm considering one or the other, and some days I prefer the 800, some days I prefer the KTM. Both are superb bikes to ride, but at least this way you've got that nice comfortable BMW warranty and aftersales treatment (something that's helped me to no end more than once). That said, KTM's parts are supposed to be cheaper? Dunno.
At this moment in time, I think if I could just go into a shop and buy an 800gs, I'd probably do it. I would with a KTM too, but I'd have to think a bit harder. All in all, I'm inconclusive