Cold Air system question !!

[Mr 5 0]

I'm not an engineer so I'm just going to give you an uneducated opinon here and that is that if the outside is hot and/or heavy (humid) the cold-air kit won't change that but since it pulls air from a lower point the air will be a bit denser/cooler and that always helps performance.
Most of the cold-air kits dyno out at about 3-4 HP gain over a stock filter system; I have the Moroso kit and it was tested by MM&FF with those results which I find to be realistic.

I like my kit ($95. and easy installation) especially at WOT (sounds like a 850 cfm carb at full cry) but I have no illusions that it makes me much faster, just a bit more efficient and that's all I expected.
Ram Air won't do a lot more for you and has some problems with sucking up water and leaves from it's low-hanging intake, but some Mustangers swear by them. Your call.