Here's some links, both text & videos.
Vortex Splash Guard
Aerodynamic Mud Flap : V-flap, Saving fuel cost & providing road safety
Eco-Flaps
Did some more reading, probably more in the order of 1.5% for the trucking area & likely around 1% for pickups & 4x4's, I just wondered if anyone had looked at them, for those that need to keep mudflaps on.