If it helps here, This was M7's try at making something close to the GP wing. Which took BMW 6 months in the wind tunnel to design . The GP also comes with a full underside body pan that smooths out the whole underside. You will find the boys at M7 now have a a rear diffuser tunnel
Here is my front I found reshaping helped .
Here are the sides
One of the biggest things I did just last month is dumped almost 40 lbs in tires and wheels which seem to have netted me 2mpg