We've had several customers over the years who wondered why Black-T costs $200 or more, and decided to have a gunsmith at another shop put on his own Brownell's-based finish. In every case, the customer eventually came back to us dissatisfied with the durability of the spray-on finish and had his gun Black-T'd. In short, based upon my experiences, I can't recommend the Brownell's finish for any harsh usage.
I've seen guns that were powdercoated. The danger here is that it is very easy to put too thick of a finish on the gun, covering up markings and making the gun hard to dissassemble (or assemble). I'm sure it's a durable finish (my aftermarket Jeep bumper is powdercoated and it's holding up well) but it isn't well-suited for moving parts, and I'd only have someone with a lot of experience and whose work I'd examined and approved of put it on.
I have no experience with the DuraCoat finish but I have been looking at their website today and it looks intriguing. I have a custom Winchester M70 Laredo-based 6.71 Lazzeroni Blackbird with a 27" 1:12" Lilja barrel AND the Laredo's BOSS installed that I may try this out on. This looks like the same finish that Springfield Armory may be using on some of their firearms (but I do not know if this is true or not).
(The gun shoots 100gr Nosler Ballistic Tips at 3,975 ft/sec chrono'd to 1/2 MOA groups and is absolutely devastating on coyotes that are call-shy and like to hang out past 300 yards. At 300 yards, it's like shooting them with a .264 Win Mag touching against them.)