The biggest reason on vehicles I've worked on isn't airspeed -- it's temperature. A large proportion of aftermarket air intakes take general engine-compartment air into the engine, which is an awful idea in a Topeka, Kansas summer with outside ambient at 100F / 38C. I am told that a lot of local retrofitters know this, and when they receive complaints, they short out a common sensor (don't remember which, don't care, I think it's one of the oxygen sensors), and the result is at least sufficient to get the complainers off their backs. This has made me quite careful about common retrofits!
But if I could route an intake using a fairly straight big hose to anything truly external and not anywhere near everything hot, I would do so as a high priority. This is why a lot of vehicles take air from a front wheelwell: it's dirty air, but it's significantly cooler than anything else available.
My Tahoe seems to split its intake from both wheelwell and underneath (not very far from an exhaust manifold), and I'm fairly certain there's an automatic flapper to switch back and forth, hopefully by temperature. I could remove all of it and replace with one big hose pointed somewhere, but where? There's just too much in the way. I could have a big slot cut in the hood, but I don't really want to compromise the OEM that much, it's a 1998 with very close to zero rust that has lived in this climate for that long, it must be from a rare run of the mill, and I don't think the gain will be worth it enough.