I admit I've not done any truly massive km in a day (650km one day was enough for an old fart), I'm with Keithblade. I think buffeting to some degree - which is all I suffer being 6ft - is acceptable, and is a damn sight better than not having any wind protection, at least. I do agree that there is instability under some conditions which might be attributable to the screen's aerodynamics (or lack thereof!), but it never gets out of hand.