It is more than perfectly fine to use leather over plate. I use leather wrists, hands and belt (Wrists - 25 Saurfang, Hands 10 Heroic Saurfang, Belt 25 Professor) and an agility ring (The one from sindragosa, I use the Ashen ring for tanking). It hurts your AP a little bit but when you end up getting 51% crit unbuffed (Well buffed I suppose with rampage being passive) and you are ArP capped so you can start using Str/Crit gems, it all balances itself out.
I also do not understand the meta bonus question =\
Edit: I forgot this was arms - you will (as others have said) want the t10 4p with hands instead of legs and try to make the crafted pants. You should also probably use the Agility back from badges instead of the strength/expertise one.
Last edited by SixStringsXD; 04-04-2010 at 10:40 AM.