well, i just finished my automotive engineering design degree and did my part on aerodynamics/ design as well ( straight A on design!!!! i just to say that)
Regarding the afforementioned wings, i have no experience, or seen them in real life so i can be absolute. The fact that the cylinder temp with the new one hasnt changed is very positive.
Just to add something to what Eatoniashoprat said, the vorteces at the back of a car MUST EITHER merge to the back of the car OR hit the road and stay attached to it at some point. only then u have a higher efficiency. if they dont attach to either they just swirl around increasing drag/ allowing the one behind to get into slipstreaming...
For our racers out there this is what all aerodynamicists try to do. to provide a laminar flow behind the car such as to maximize efficiency AND minimize the distance that this happens or in other words how close the guy behind can come to take advantage of the slipstream phenomenon.
On the combined use part... i think that if u investigate/research/design a roof spoiler and a wing u can achieve maximum downforce by directing the vortices leaving the roof spoiler to be at a small angle to the wing. so u get rid of the laminar flow at he back, only to direct it onto the wing.
one would say that this wouldresult in a maximum pressure on the top of the wing, and no air flow below. if u know what u r doing, then the vortices will still be at an angle to the wing, but fall in front( cross the horizontal plane in front of the wing) of the wing, and with the wing a turbulence will result at the bottom wing surface. i hope u r still with me. if u need i can draw it. aerodynamics is a language spoken with pictures and sketches etc...
sorry for the long post guys. i just like explaining things ( they r still fresh)
Chris