Has anybody spent any time measuring the air pressure at various points around the car while it's in motion using something like a Magnehelic gauge? If you're feeling fancy you can probably rig up a bunch of barometers and log it with a laptop.
To oversimplify the complex and unpredictable subject of fluid dynamics, air flows from higher pressure areas to lower pressure areas. Consider your tires, they're inflated to a relatively high pressure. When you open the valve air flows out into the atmosphere, the only way to add air is to connect a source of air that's pressurized to a higher level, such as a tank containing air compressed at a higher rate than the tire.
This is the best picture I could find....
The red spots are high pressure areas. Our cars are obviously not those, but they'll share two things, the high pressure area at the front bumper and at the base of the windshield (cowl).
So if I were having cooling issues, I would want answers to these questions...
1. what is the pressure differential between the various points in front of the grill (upper and lower) where air is meant to enter the engine bay, and the various points between the radiator and the drivetrain
2. what is the pressure differential between the back of the engine bay at the firewall and the base of the cowl, with the rubber strip on and off the car.
3. what is the relationship between those two points, as in... if the weather strip is removed does the pressure differential between the primary cooling hardware at the front of the car become less favorable
Regarding #2, I feel that is it a near certainty that the air pressure at the base of the windshield is higher than the pressure at the back of the engine bay. That means that air would be entering the engine bay at the base of the windshield instead of leaving it (this is why the vents for the interior are in that spot). This might be beneficial, maybe removing the strip increases airflow through the back of the engine bay and out of the bottom of the car, helping push the hot air around the turbo out.
But, what #3 would answer is..... that it might be counter productive. Raising the air pressure at the back of the engine bay might be having a negative effect at the front where your main heat exchangers are mounted.
The hooded vent on Lao278's car absolutely makes sense. He's created a low pressure escape for the air that entered through the grill of the car. He's created more airflow through his cooling stack and it worked.
A thought regarding the placement of the aftermarket oil cooler.... is right in front of the condenser really the best spot? Some MkVs could be had with auxiliary radiators located behind the bumper cover on the driver's side (US)...
http://www.golfmkv.com/forums/showthread.php?t=117682&page=5
There's surely plenty of room to fit an oil cooler in there. Remove the fog lights, put holes in the plastic trim, add this behind it...
Your radiator would probably be a lot more effective if you weren't sending air into it that had already passed through an oil cooler with 240+ degree fluid running through it.
Then there's this...
Yeah that's the R32 belly pan, but the stock one has NACA ducts in those same spots. If you go with a high quality, durable plate and fin oil cooler that seems like a safe place to try to mount the oil cooler as well.