Protection Warrior dps isn't going to be anything worth writing home about. It is what it is and it is quite bad - well below what the other tanking classes can do. When you ask a protection warrior to dps (in protection spec) what you're really asking is "would you mind staying in tank gear in case the other tank gets wiped and just auto attack while you read a magazine?" And since prot war dps really only is "tank wipe insurance" you're probably best to remain in tank gear.
Now, if pure dps is what is needed then what you might do is just dual-spec with arms or fury for those times when only one tank is needed. That is the only way you'll really contribute to dps while providing sunder/demo/clap for non-warrior tanks.
Dual spec is the only way to go really. Prot war dps doesn't exist afaik. This is my approach to 10/25 man raiding at least with my warrior. I can tank or dps...but I can't tank and do dps. I have to swap specs otherwise I'm just tank wipe insurance and you're 9/24 manning the boss b/c I don't really contribute much other than class debuffs.
Former healbot now a Disgruntled protection warrior.