Hey samh. This is my first post here. I registered specifically to be able to reply to your post.
Short story: I was able to mount the Parabellum F650GS/Dakar post '05 windshield on my G650GS.
Long story:
I went through all the windshield alternatives I could find on the internet, looking for something that would offer protection for highway riding. The parabellum was the only thing I saw that looked like it would work for me. I called them too, and they told me they had not had a G650GS in their shop to try and fit a windshield to, but that they had one negative report from someone who had tried it.
In talking with the parts guy at the local BMW dealership, I found he was amazed that should be the case, since (he claimed - rightfully as it turns out) that all the handle bar parts are the same. The dealership has a link on their website to the BMW online parts catalog, so I went to the catalog and compared part numbers between the latest model F650GS/Dakar and the G650GS for the handlebars, everything that attaches to the handlebars (including the hand protectors, switch clusters, mirrors, grips, grip heaters, handlebar weights - all of it). I did the same comparison for the instrument cluster and windshield. All the part numbers that I compared were identical across the F and G models. Knowing that, I took a chance and called Parabellum -representing that I had an '07 F650GS- (so I didn't have to listen to them tell me again it wouldn't fit), and ordered their 2005 -on windshield for the F650GS.
http://www.parabellum.com/stores/showde ... 51&CATID=1 I was able to mount it just as the instructions told me to. I followed the instructions for the later model F's, and used the spacers they include and specify for those models. Like Parabellum says in their mounting instructions, there are an almost infinite number of adjustments that can be made, since everything from the angle the handlebars are mounted at to the angle the hand protectors are mounted at, along with how you adjust the windshield mounting hardware, will affect the final fit. I was, however, able to get everything adjusted without a lot of trouble.
The one thing I do not like about the windshield is that it contacts the instrument cluster housing when the handlebars are at full stop. It scratches the housing at the point it makes contact. Parabellum tells you this in the installation instructions, but not in the sales info on the website. This probably isn't a big deal if you don't lock the handlebars, but it definately made scratches on the housing when I put the handlebars over to lock them. - Maybe that means it doesn't really fit, but if all the parts are the same, I'll bet it does the same thing on the F series bikes.
For what it's worth.