540 defense is the minimum. After that stack stamina and armor. You get enough hit and expertise on your gear (or you don't, but it doesn't matter since threat is moreso based on your rotation and spec than any gear). Also the expertise softcap is 26 not 25, hit cap is 8% for melee.
I would also like to add that you're missing out on a fair bit of effective health with your gemming. It's all personal preference, but I would make the following recommendations.
I would recommend replacing the AP/STAM gem in your shoulders with EXP/STAM or pure STAM. The socket bonus on the locak (+6) is below the threshold that most use to match colors, I'd replace with STAM. I'd also take the 20 HIT gem out of the bracers and use HIT/STAM or DEF/STAM if you want the bonus, otherwise pure STAM. The gloves are lacking any bonus health from gems and you could replace one or both that with STAM or some hybrid that provides a threat supplement.
Rimefang's would also benefit from Bladeward, Mongoose, Blood Draining. Titanium Weapon Chain is a cheap one to consider too if you don't wanna invest alot in the short term. Gives you more hit I believe.