In the below thread is a test I did to see exactly what the under the Hood temp was (Post #5). What I found out is that as long as the Car is moving; even in City Traffice the outside and under the Hood Temp are about the same.
Only when the Car sat and Idled did the under the hood temp rise (98-110 degrees F).
Hot Air building up under the Hood at Idle is not causing any performance issues and the under the Hood temp drops quickly when the Car is moving; so, I believe there is no performance disadvantage to having the Air Filter drawing Air from under the Hood.
Replacing Stock Air filter with straight flow cone k+n?
Also the above is a different issue from cooling the Air compressed by the Turbo with an After/Intercooler.
When I get around to it I want to stick the Probe inside of my Intake Manifold and see just what type of temps are there due to the Turbo.