In a way of looking at it, all an economy is, is the "changing of ownership" of goods, many times, circulating around a network. The decay of items, over time, is what destroys the goods. They may exchange hands but they will still break and need to be replaced. Even good pvpers die and lose gear. Even good pvpers will break their gear. They will never
not need a supply of it supplemented from trade.
Even the best fighters in darkfall with all their top-end gear have to do
some trading, because you get people who purposely "pre-break" their good gear from duels, so they can use it in a real fight and spite the enemy with nearly broken loot in the chance that they die. Otherwise, they can't sustain themselves only on the good gear of those they kill. They need to trade for it too.
Faster than not at all
Ideally, fast enough that active pvpers would need to replace their gear within a week of pvping daily. Harder to put a speed on decay for crafting in this game, that might just be a matter of trial by fire.