Not sure I buy into one being worlds better than the other. KTM has great off-road rep and know how but in the really rough stuff weight/size counts for a lot and the 800GS is remarkably light and nimble for what it is (and ~50 lbs lighter than a 990). I think either would do fine within the noise of rider capability.
I don't need another bike than the FZ but I bought a old XT350 dual-sport b/c it will be fun when it's running again. I've been lusting after more adventure-type bikes for a while also. At the end of the day, I figure 5 bikes would be about right - a naked commuter, a dual-sport/motard, a sport-tourer, an adventure bike and a super-sport.