All current production cars I know of have cold air intakes, no one pre-heats anymore, since they don't have carbs to freeze up.
5-20 hp is only going to be available a WOT, and I almost never drive that way -- can't affort to blow an engine just for fun, I work for a living.
Hp increases from fancy intakes usually have more to do with less flow restriction through the filter housing, and concommitant higher noise levels, not better flow through the filter.
Do as you please, I'm prefectly statisifed with the stock filters.
And PLEASE, this isn't 1950 when Detroit would stick a 1 barrel carb on a flathead V8, ALL intake systems are engineered, not scribbled on the back of an envelope after a long drinking session at the strip club...... Quiteness of operation, engine longenvity (people DO expect the engine to outlast the second lease payment, after all...) and ease of service are all part of the equation, along with horsepower output, cam timing, exhaust backpressure, milage requirements, etc. It ain't just a matter of "lettin 'er breathe more".
All oiled foam aftermarket filters allow more dirt through than OEM (NOT cheapo aftermarket filters!) paper filters, and all will trash a flow sensor if the oil gets down into intake, as it will if you oil it enough to actually trap all the dirt. OK the first time, but the second "two months without beer because the $600 MAS got trashed" isn't that much fun anymore.
These are NOT the same as a real oil bath filter, which is MUCH more efficient at removing dirt. Not at allowing air flow, but he really do remove dirt. They also oil the intake nicely, no one has used them since the early 70s, and I think Benz was the last holdout.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!