Sorry, I'm too lazy to look at the wow-heroes thingy, so I'll just answer the questions you have in your post.
ArP isn't linear, that's what makes it so hard for people to understand it's value. It's weak at lower percentages and gets better the more you have.
Get the relentless earthsiege meta gem, it only needs 1 nightmare tear to activate.
I agree on head/shoulders for t10 2p. Get the Gatecrashers Gauntlets and blood-soaked saronite stompers (if you don't have it already).
I wouldn't mind sacrificing haste for ArP and then gem for hit. The most important thing is to get your ArP up and stay on the hit and exp soft caps.
I don't have 4p t10 yet so I'm not going to try and explain it
Oh, and, RAAWRARAWRAWRAWR LOSE UW!!!!!!!!!1111oneone Get booming voice and commanding presence instead (lose imp. cleave aswell, you don't need it for boss fights). Also get Heroic Fury, its awesome.
Hope that answered some of your questions.