A new mythbusters episode was on tv and was about getting caught in the rain with a cab and flooring the car so you dont get wet. The car the used for the test was a silver s cab with sport crono, and a few other options, from what I saw you can get close to beating the rain
thought some might be interested

 

if they used the wind deflector it would have been amazing.. i drive here in florida on the highway with top down all the time and it usually rains along the way...

top down, windows up and deflector up the rain doesn't hit anything but the top of the defector and the top of the top in the back thats covered... they did top down, windows down, no deflector.