Thanks for the replies people
I think the downforce theory is made up... think about wings on cars and planes - you need a wing/winglet with air flow tuned on each side to generate a vacuum zone underneath in order to pull down and above in order to pull up. The mere presence of an angled piece of plastic such as a front fairing doesn't mean you get the vacuum zone pulling down. What you do get with that fairing is a bit of extra weight over the front and slightly further forward centre of gravity (prob a few mm, maybe a cm at the very most?) which may make a difference to handling, but whether that is noticeable or not I don't know. Riding position would likely have a greater effect on all this would it not? Prob better air flow on the F at high speed to make it more stable, but I'd say it's unlikely to be downforce.
So far so good with mine, but only been up to 70mph. Running in is a very dull affair!