I was hoping to do pvp as prot too but suspect it might not work out. Damage trumps defence in most pvp (people will just not target the tank if there's another target) unless it's a tank role (FC) and we still have the damage debuff if we flag carry as a tank.
I stumbled on Wintergrasp this morning in prot spec and tangled with some level 98 NPC guards. I felt my self-healing was just not strong enough (I had talented sacred shield), so I switched to ret and found it much more comfortable bursting them down and healing myself up with FoL. I did not fight other players, but I went ret partly because I thought it would be better if I did - more damage AND more self-healing. But this is only very casual opinion - I'm not a pvper or theory crafter.
Did alot of test and fought alot of people trying prot. Its subar even as a FC. It doesent have mobility of a druid and less survivability then a blood DK. Blood DK has damage almost comparable to a warrior in pvp. I was running around critting clothies for 15k death strike during war games, prot paladin im not so lucky. I can solo prot paladin on my rogue with little trouble, blood dk on the other hand its like grinding a raid boss that i can eventually kill given 5 minutes alone with him if i avoid damage perfectly.