At 5'11 the '10 windscreen on my '09 was a huge improvement. It puts me in bubble of perfectly calm air and is a big aid to keep the chill off on those cold days. All the way down this summer to provide a blast of cooling air.
For me the '09 screen didn't do anything particularly well except look good.
I am of about the same height and I found the OEM 08-09 screen to be too short for long rides. The OEM 10+ screen was much bettter. I ended up with a V Stream screen which is taller still and this one gives me all the protection I need. I have C Bailey's ultra dome shield still in a box (never tried it), but I think I will never use it.