Yes it has to be under 4" to stay legal where I'm at. Price is not really an issue since it'll be my main carry.
Any thoughts on 5160, 52100, or L6?
I may be looking to have it custom made since I have ideas the handle a manufacturer might not offer.
5160 is one of my all time favorite steels for knives, as it's very tough, springy, not prone to chipping, and it takes and holds a good edge. You'll probably want to oil a knife made of 5160 from time to time, unless it's coated, to keep rust at bay, but unless you live near salt water or have really acidic sweat, it shouldn't be a problem.
1095 is very similar to 5160, except that is is
slightly less tough and springy, but it holds an edge a slight bit longer.
As for the other two steels you mentioned, I don't know anything about them, so I can't help you there.
My recommendation for a take-anywhere, under 4 inch blade survival fixed blade would be the RAT Cutlery RC-3. It's made of 1095, with a coated 3.5 inch blade. It also comes in rather unique color schemes.
Also, since you said price was no concern, I'd take a look at a Busse Game Warden. It has a 3 inch blade, and comes in different thicknesses. As for the steel (INFI), there is none better as far as toughness goes.