It looks like your diving pretty deep. Your proposal (in white) looks like a pretty standard Kammback such as you see on Metros, etc., with proper curvature.
I'm really skeptical about that 'novel spoiler' in yellow. It's on a ~10° slope to start, there will be no laminar flow there to fill that narrow throat at A. It's a diverging duct. It might work better if it's cut back to B and convex from B to C.
But that's what wind tunnels are for.
As far as aerohead's quote, I'd point to Morelli's Fluid Tail.
His post is Photobucketed, but here are links to the Morelli paper:
A New Aerodynamic Approach to Advanced Automobile Basic Shapes
SAE wants $28, others will let you download it. It shows the FIAT Punto.
edit:
Of course as soon as i hit submit, I proceed to find this thread from 2008:
http://ecomodder.com/forum/showthrea...info-2072.html. Here's Morelli's Punto
