I have tried full guards.
This was my first commuter:
Heavyweight steel monster:
But then I went lightweight
And I honestly don't really notice the difference. In Wales, when it rains, you know about it, regardless of guards. Wear effective clothing instead.
I'm going to start wearing shades though as I took the long way home last night down some tiny back lanes and seemed to be getting hit by flies at 30MPH all the time. One in the eye would have been nasty.