Word from a more or less poor player ... take advice with grain of salt.
I'm only 110 on my DK, but I find that anything that reduces skill recovery/cooldown time is a plus. My weapon SA is even set to skill cooldown at the moment. The DK's skills are its hallmark, so anything that gets those going as frequently as possible or as long as possible is what you want.
Also, don't skip on items that increase your PDef, although that doesn't necessarily have to be at the top of the priority list. My DK was squishy until I made a +10 Levi set and added Tersi 5/6 and armor augments to him. The role of the DK, though, is to deal massive AOE damage, so don't break the bank on this. There are lots of ways to add pdef without plopping down billions on Protection talismans or Diamond jewels.
I don't know if my current setup will work at 113+, but I do ok for now with help from buffpet.