I am interested in switching to an Armor Pen Marksman Hunter. No, that's not quite right. I'm interested in the number crunching to determine on paper if I would rocket my DPS through the roof. The calculations don't look that favorable. I could increase my DPS, but not like a rocket. And I'd give up a lot of utility.
I have an armor penetration rating of 419 from gear. That doesn't sound like a large number when our hard cap is 1400. That is usually from prioritizing Crit over ArP.
I have 20 regular gem slots at the moment. 17 of the 20 slots are slotted with agility. If I swapped 19 of them over to ArP it would land me with a total 799 ArP rating. It would only cost 3,800 gold if I got the raw gems and had someone cut them.
I only have the crappy ArP proc'ng trinket. I probably can't get the raid one, but I could fairly easily get the better five man one. Even still, that is only the soft-cap on-proc world. Not exactly stellar.
And there's that 3,800 gold buy-in with a 3,800 gold reversal fee...
EDITED TO ADD: Oh! And I'd probably feel compelled to put on two of my T9.5 pieces again. I haven't studied it vs the T10x4 bonus.