IF your goal is ultimate top speed, you know de-restricted running up around 190 or so an after market screen and it's effects on aero dynamics could be a concern. But in the real world it comes down to a couple of things. Are you short enough that you can see the tops of your gauges with the stock screen in place? And are you satisfied with how and where the wind hits you with the stock screen?
Replacing the stock screen is a simple and quick way to alter the looks a little, (I think for the Better) and give you a little better wind protection while letting you see all of the gauges...