So I'm on the PTR, and from what I understand at level 80:
Exptertise Cap = 6%.
42.66 Expertise Rating = 1% Expertise, so 256 Expertise Rating for Cap.
Melee Hit Cap = 9%
32.58 Hit Rating = 1% Melee Hit, so 293.22 Hit Rating for Melee Cap.
Spell Hit Cap = 16%
26.13 Hit Rating = 1% Spell Hit, so 418.01 Hit Rating for Spell Cap.
So if this math is correct, I'm just wondering if there would be any point to grab enough hit rating to be both melee and spell capped, or only worry about the melee?
There is no longer Melee Hit and Spell Hit ratings (and also melee crit and spell crit rating); all of them has been merged into an unique rating stat.
Considering the fact that we have to deal with expertise and armor penetration (caster only with spell penetration) I think we had to consider only the melee cap.
In other words I think also for retribution paladins the melee and spell hit ratings are equals.
Is armor penetration even going to be that useful for us? Currently on the PTR I've been focusing on getting hit and expertise capped, while picking up haste where I can.
I don't know if while leveling 71-80 (and of course from level 80normal/heroics) a ret paladin can build up some "paladin equipment" (just for now ret paladin equip is just a piece of warrior equip with a +int bonus).
If you just share pieces with warriors it will be completely natural to have to raise armor penetration because nearly all warrior pieces have this stat.