Since we've started this project bike, the most frequent question I've been getting is "so how do you like the 990 vs the GSA?"
I can tell you it's been a lot of fun! I really like what is obviously better off-road handling and the highway comfort is not as bad as I expected (my Seat Concepts seat sure helps!). While I love my GSA too, I can't say that I'm missing it that much yet.
There are a few interesting surprises though that I didn't expect. For example, I thought the 990 was like 100 lbs lighter or something but the specs show the dry weight is just 32 lbs lighter! Also, the 990 has loads more travel, right? Nope. Only with the 990 (R spec suspension from Konflict) has front/rear travel of 248mm/248mm vs the GSA's 210mm/220mm! My stock 990 Adventure came with 210mm/210mm; about the same as the GSA (less in the rear).
The center of gravity is also much higher and that, combined with less front end feel (suspension is so good), and you'd best be light on that front brake or you're going to low-side really damn fast! Ask me how I know!
The gearing is also taller than the GSA's legendary tractor gearing, but that's easily addressed with larger rear and smaller front sprockets.
Bottom line: Much better in the dirt and not as bad on the highway as expected.
Pro's: Lots more off-road fun, feels more powerful, nimble, suspension doesn't bottom out (my TFX Suspension on the GSA doesn't either anymore)
Con's: Really tall, taller center of gravity, taller gearing, sucks gas big time when you're on the throttle.
* I should note here that this switch was due to type of riding I like most. I was looking for something not similar to the GSA but 21/18" wheels, more travel and more dirt-able. The 990 has not fallen short of my expectations, I can assure you.