Had the opportunity to test the two bikes back to back yesterday. I know its been done to death but I'd give my ovservations for reference:
Looks
I guess the GSA has it on the looks department. Certainly gives the Tonka toy look. When riding around people turned to look at me on the GSA whereas didn't really give a toss on the GS. When filtering oncomming traffic made a beeline for the gutter
Weather Protection
Well it was one of those drizzly days, so not particularly pleasant. Did a bit of dual carridgeway work (A31) then some twisties (Alton - Basingstoke). The screen on the GSA is better than the GS, but not to the degree I thought it was be. If I had to quantify it, I'd say 25% better in terms of noise, blast, buffeting etc. Leg protection however was much much better on the GSA. I didn 't feel as though I was getting the wet left leg syndrome, but I could have been imagining that. Overall my legs were nice and warm on the GSA, but not on the GS.
Riding
The steering of the GSA was definately much slower than on the GS. I didn't get to go on any slow twisties, but would guess it may be a slight handicap on those rodes. On fast twisties it felt more planted than the GS. However, it depends on whether you like the 'planted' feel. When swapping to the GS, I was much more aware that it was a more 'exciting' ride. The GS wheelied off the trottle over bumps and exiting corners when gassing hard. You didn't get that with the GS.
I was certainly aware that the GSA was taller. When you're riding along it does feel like a GS on stilts. That part of it was actually quite fun. At 5'11'' I was on the verge of not being comfortable with the standard seat. I had to reach down with my feet to find the ground rather than it just being there. I would think that it would be easy to come a cropper if getting on a slight camber. It would have been better with the standard GS seat I guess I think that the ride over bumps was slightly better on the GSA, but there wasn't a lot in it.
Performance
Simply put, the GSA felt like a GS with loaded panniers. It was certainly held back by the extra weight. Again, there's not a lot in it, but the GS had a bit more 'urgency' about it. Not enought to put me off the GSA however.
In comparison to the '04 1200GS that I used to have I noticed that the torque speed curve was much more linear. There used to be a dead spot around 4500rpm then it would surge at 5000+. This dip is no longer there (or reduced so not noticable). This make higher rpms more accessible and hence the bike now feels simply 'faster'.
I think that because of the better weather protection there is a tendancy to go a tad faster on the GSA than the GS.
Comfort
For some reason I felt that the GS seat was quite a bit more comfortable than the GSA seat. The GSA forces your legs apart due to the tank I guess, whereas your legs are a bit closer together on the GS. For this sole reason the GS was the more comfortable bike.
Other things
I kept catching my trousers on the GSA pegs. Maybe something you'd get used to, but a pain during the test ride.
I didn't fill the tank up to anywhere near its capacity, so am a bit unsure as to the effect this would have on handling.
Spoked wheels look a pain in the arse to clean
Summary
There really donesn't appear to be much in it. The GSA has the advantage of better weather protection and range, whereas the GS certainly feels 'faster' and more fun the ride round town and on the twisties. I thought that the two would be drastically different bikes but there's really nowt in it.
RT
Had a go on an RT back to back with a GS a few weeks ago. Did the rest ride in the pissing rain. You can ride around on the RT all day and stay virtually dry. The only thing that gets wet is your back due to the low pressure behind the bike. I came back off the RT test ride thinking it wasn't too bad. Got on the GS and literally within 50yrd realised I wouldn't want an RT until I was retired
Looks
I guess the GSA has it on the looks department. Certainly gives the Tonka toy look. When riding around people turned to look at me on the GSA whereas didn't really give a toss on the GS. When filtering oncomming traffic made a beeline for the gutter
Weather Protection
Well it was one of those drizzly days, so not particularly pleasant. Did a bit of dual carridgeway work (A31) then some twisties (Alton - Basingstoke). The screen on the GSA is better than the GS, but not to the degree I thought it was be. If I had to quantify it, I'd say 25% better in terms of noise, blast, buffeting etc. Leg protection however was much much better on the GSA. I didn 't feel as though I was getting the wet left leg syndrome, but I could have been imagining that. Overall my legs were nice and warm on the GSA, but not on the GS.
Riding
The steering of the GSA was definately much slower than on the GS. I didn't get to go on any slow twisties, but would guess it may be a slight handicap on those rodes. On fast twisties it felt more planted than the GS. However, it depends on whether you like the 'planted' feel. When swapping to the GS, I was much more aware that it was a more 'exciting' ride. The GS wheelied off the trottle over bumps and exiting corners when gassing hard. You didn't get that with the GS.
I was certainly aware that the GSA was taller. When you're riding along it does feel like a GS on stilts. That part of it was actually quite fun. At 5'11'' I was on the verge of not being comfortable with the standard seat. I had to reach down with my feet to find the ground rather than it just being there. I would think that it would be easy to come a cropper if getting on a slight camber. It would have been better with the standard GS seat I guess I think that the ride over bumps was slightly better on the GSA, but there wasn't a lot in it.
Performance
Simply put, the GSA felt like a GS with loaded panniers. It was certainly held back by the extra weight. Again, there's not a lot in it, but the GS had a bit more 'urgency' about it. Not enought to put me off the GSA however.
In comparison to the '04 1200GS that I used to have I noticed that the torque speed curve was much more linear. There used to be a dead spot around 4500rpm then it would surge at 5000+. This dip is no longer there (or reduced so not noticable). This make higher rpms more accessible and hence the bike now feels simply 'faster'.
I think that because of the better weather protection there is a tendancy to go a tad faster on the GSA than the GS.
Comfort
For some reason I felt that the GS seat was quite a bit more comfortable than the GSA seat. The GSA forces your legs apart due to the tank I guess, whereas your legs are a bit closer together on the GS. For this sole reason the GS was the more comfortable bike.
Other things
I kept catching my trousers on the GSA pegs. Maybe something you'd get used to, but a pain during the test ride.
I didn't fill the tank up to anywhere near its capacity, so am a bit unsure as to the effect this would have on handling.
Spoked wheels look a pain in the arse to clean
Summary
There really donesn't appear to be much in it. The GSA has the advantage of better weather protection and range, whereas the GS certainly feels 'faster' and more fun the ride round town and on the twisties. I thought that the two would be drastically different bikes but there's really nowt in it.
RT
Had a go on an RT back to back with a GS a few weeks ago. Did the rest ride in the pissing rain. You can ride around on the RT all day and stay virtually dry. The only thing that gets wet is your back due to the low pressure behind the bike. I came back off the RT test ride thinking it wasn't too bad. Got on the GS and literally within 50yrd realised I wouldn't want an RT until I was retired

)
, so its not an issue for me