Hi Dolo, I sold my GS300 after about 6 months for the same reasons. I too found the ride unbearable. I had a Sport and so expected the ride to be firm, but I found the way it crashed and banged over uneven road surfaces and skipped across the road when going around uneven corners unacceptable for a car of this class. I also noticed the wind noise, but that wasn't a major reason for selling.
I loved a lot of things about my GS. The looks and individuality were far better than the BMW 528i which I owned previously, as were the smoothness of the engine and gearbox. It was also a really comfortable place to be on a long journey (as long as the roads were smooth!). The handling wasn't as good as the BMW, but I knew that before I bought it.
The ride quality in my Audi S3 is actually better than in my Lexus. Everyone I know who has been in both cars agrees with me on this. The Audi has the firmer ride, but it handles uneven surfaces and potholes far better. This really surprised me - a hot hatch with better ride quality than a luxury saloon!