I'm 5'10" with a 32" inseam, and the stock screen's turbulent air hits me just below the chin at freeway speeds. So my head is up in the clear air. At freeway speeds it's still noisy, but I always wear ear plugs, and at least my head isn't getting whacked around.
I plan on staying with the stock screen for several reasons: I like to ride off-pavement, mostly out in eastern Oregon and Nevada, where it can get plenty hot in the summer, and the flow of air over the short screen will be welcome. My experience with a larger screen on my Wee taught me that it's a real negative in that type of riding, and I almost got guillotined once riding through Titus Canyon in Death Valley when I hit a rut hard which threw me forward into the screen. Only the low chin bar on my helmet literally saved my neck. And large screens tend to flop around violently in that type of riding as well, putting a lot of stress on the plastic mounting points.
Now if most of your riding is at high speeds on slab, especially in colder weather, I can see how a larger screen would fit the bill. But for me the negatives outweigh the positives.
I'm tryin' ta think, but nuttin' happens!