It's still an amazing stat when you get a lot of it. The ArP Cap becomes 1400, so you need 735 + Mjolnir, or 788 + Grim Toll to soft-cap it, and probably shouldn't gem it at all unless it puts you over 500 + trinket. The point at which you drop the trinkets and go for strait ArP is around 1k ArP.
would that be 500+ without the trinkets or would you need 500+ AND one of the trinkets to make it worth while? i only ask cause thats the postion i'm currently in. 531 armpen (socketed), but havent been successful in acquiring either trinket so far.