So, the stock windshield on the R1150GS isn't that good. It allows a fair bit of buffeting and not much actual wind protection. Many people have spent many hours over on Adventure Rider (
http://www.advrider.com/) discussing solutions. I first tried the Tobinators (
http://www.stopthebuffeting.com/) and they helped with the stock shield for sure. They are extremely adjustable. Then I bought a used Cee Baileys screen. (
http://www.ceebaileys.com/cycle/) It at least 4 inches (10 cm) taller than the stock shield. It really helps too.
After much riding, including a four-day ride through the southern interior of BC last summer I've decided to sell the Tobinators and keep the Cee Bailey shield. I think it provide the right level of protection that I'm looking for. I even tried the Tobinators and the Cee Bailey together but it was just a tad unstable because of the additional height of the shield.
I may even put the stock shield back on for the summer months, once the temperature gets up above 20C regularly.
Another thought is to possibly buy another stock shield from BeemerBoneyard (
http://www.beemerboneyard.com/) and cut it down by 40% for the summer months. That might provide the best option for smooth airflow albeit at the expense of protection.