I see you have several several +20 Def gems and a +20 Hit in your belt. I assume thats to get over the def minimum of 540, but you also have 50 points of Resilience from your shoulders. So, you could drop a couple of those and put +30 sta in for them. 490 def + 50 resilence would keep you crit immue.
For a prot warrior, your better off going for expertise over hit, so I'd loose that gem also. But, if you really want to keep it or get the socket bonus on your chest, put it there, but you'd be better going w/ a +def/+sta gem. The general rule of thumb for socket bonus by alot of people, is if it's less than a +9 sta bonus, your better of to go for STA(i.e. blue +30sta).