I've got a Cal-Sci windscreen (with stock cut outs) and hit some fairly robust showers recently, but didn't notice any "abnormal" amount of water leaking through. After slowing below about 30, everything is going to get wet, but the cut outs in my opinion, didn't leak enough to be an annoyance.
I just did this to my stock windscreen with ok results. The increase in airflow over my Cal-Sci is noticable, so much so that this will be my warm/hot weather windscreen for the time being. The only beef is that although back pressure is eliminated, it still cannot provide the quiet air that my Cal-Sci does. The stock screen windblast at full up position is still hitting me at chin level so in order to get in quiet air, I need to hunker down behind it (read sportbike like crouch). I'll use my Cal-Sci for long distance when I want to hear my tunes clearly, but the stock one looks better and provides the needed airflow for my Stich' to help keep me cool.
For my height & riding position I say yes. As far as I'm concerned, the unmodified stock windscreen is worthless. However I have a Cal-Sci for cooler weather or when I want a "really" quiet ride, which just cannot be acheived with even the modified stock windscreen, but it's MUCH better than without the cutouts. Again, as many say YMMV.
