It wasn't a GSA but I had an 1150GS until December, and have had an 800GS since then on which I've done 4000 miles. Most of my trips are 25 - 40 miles each way, though I've done many longer ones and a few 170-180 mile journeys.
I loved the 1150GS, but I'd keep the 800GS over it anyday. Possibly because the 1150's saddle had endured 50k miles, but I didn't find it any more comfortable than the 800's. The 1150 offered better wind protection (I had the GSA screen), but I'm still happy with the 800GS on the motorway when I do go that way.
The 1150 had more torque and was better for lazier overtaking, but I enjoy being more involved in riding the 800. It still has plenty of poke for overtaking, but you might choose to drop a gear to really get it shifting past.
There's no contest when it comes to filtering.
With enthusiastic use of the throttle, my long-term average fuel consumption is 53 mpg, but I've not yet broken 200 miles range from a tank (192 miles when I deliberately ran it dry to find out). I've tried, but can't get 65 mpg for any length of time like some people claim, and I can't be arsed to ride everywhere at 40 mph. On the 1150GS, my fuel consumption mpg was normally in the high-30s.
Having also ridden a number of miles on a 1200GS, I can't see myself going back to one of the big GSs. The 800GS is, imho, far more fun and just as good if not better in many areas than its bigger brothers.
