How much Spell Penetration for PvP?

[Kreuz Kontrol]

I did a bit of looking around on the forums and even tried Googling, "Spell Penetration in Cataclysm" but I could not really find the information I was looking for.

What's the "magic number" for Spell Penetration in PvP? I'm going to guess that it's 195 to negate the Priest "Shadow Protection" buff, but I would like some clarification.

Assuming it is 195, then I'm guessing all we need is http://www.wowhead.com/item=64808 and maybe a spell penetration gem and/or cloak enchant? The neck piece offers 179 on its own which is really nice imo.

[Deleted]

I would say 120 to land the dispell that removes the priests shadow protection