even with cold air ducts etc, the engine bay temps will average about 80 deg F, and witha sealed kit you can hlaf that, which is where the real power gains come in. INcreases in flow are minimal, the std one is not restrictive in the least.
Head shields do little as heat soak through radiation is nto the problem, ambient air temps are the problem.
I woudnt mess about with open cone types, just not worth the money and loss in power....
As for filter restriction. You can get by increasing flow without making the filter less effective, increasing surface area is the simplest way, but foam and cottom gauze types use oil as the fikter and the foam/cotton as the structure to hold and store the oil.