I had K60 Scouts on a Transalp last year and did a round trip to the south of Spain on them. As stated, for the first couple of hundred miles they move around a lot and make you think there's something wrong with the bike. But they settle down. While the Transalp is about the same weight as a GS it's got a lot less power. I did about 3,500 miles on the trip and I'd say the rear tyre was half worn (squared off) when I got home. Being squared off didn't seem to affect how it handled, though, which I found strange (but good!). And I did over 2k miles of motorways at rather enthusiastic speeds (particularly for a Transalp) so squaring off was pretty inevitable on any tyre.
These tyres absolutely don't have the same grip as a road-oriented tyre or even something like a Tourance. They're amazingly good for something so knobbly but they are not miraculous or witchcraft. I was riding with a friend on his rented 1200GS LC (with Tourance EXP or Next - can't remember) and trying to keep up with him on the roads around Ronda was interesting. I didn't have the GS grunt out of tight corners so was riding pretty hard to try to keep with him. The tyres were the limiting factor, particularly the rear. It was the first time in nearly 30 years of riding that tyres, rather than my own ability, were the limiting factor in how fast I rode. They were squirming at full lean and I had a couple of moments, although they probably weren't as severe as they felt. Enough to make me back off, though.
For the right type of riding the K60 Scouts are good but for pure road riding, particularly if you like to ride at enthusiastic speeds on twisty roads, they are not the right tyre. I wouldn't consider them for my GS based upon my experience, but then I have no intention of taking the GS offroad (I did with the Transalp). Take with a pinch of salt anyone saying these are the best tyre they ever rode on. They may be the best compromise tyre for some people who take their bike offroad but an unreserved 'best tyre'? I don't think so.
