Poodles, i know this subject has been beat to death. And im not going to get into a discussion about it. i will continue to run my 7m's this way. I have never had any dextrimental effect on cooling whilst the car was driving, and considerable lower under hood temps while stationary or in slow moving traffic.
My reasoning, well its Suffice it to say that the air which passes through the radiator is at high pressure (due to the stagnation point at the front of the vehicle). The air looses some pressure as it squeezes through the air passages of the radiator, but not that much. After that this high pressure air is "trapped" inside the engine compartment, with no where to go except down and out around the engine. Meanwhile the air which does not pass through the radiator mostly flows up and over the front edge of the hood. It must speed up to make this journey (and still conserve overall mass) thus the local pressure goes down. Add to this the fact that the air possibly separates into a local eddy as it turns the corner over the front edge of the hood and you have that there exists a local low pressure zone along the front portion of the hood. The net result of these flow patterns is a large plan area (the hood), with high pressure underneath it (pushing upwards), and low pressure above it (sucking upwards). Rasing the rear of the hood will vent the two pressure regions together. Let the high pressure air vent out to mix with the low pressure air.
Now i dont have a virtual wind tunnel, or hard data But It works for me and i'm happy. If i was driving a $90K track car, then i would be concerned about the pressure zones, but only for Aerodynmaic reasons. So i guess its each to their own, im happy with it.