Switch to blood asap so you can get experienced with it. Don't worry, you don't need tons of arpen to do it well; I was outdamaging unholy DKs long before I stacked a decent amount of arpen (though my current arpen isnt amazing.)
Khelek is also mistaken; the theorized 6200 ap inflection point is to make Arpen > STR, not Arpen > AP. This would make Arpen the most valuable stat you can find on gear for Blood.
Also: Try for Mjolnir Runestone over Grim Toll. They're both great but hit is so damn easy to cap.