Posted this in the PvP forum, but I'll re-post it here: http://imgur.com/Ulzz5
That's nearly 500k damage as a 31/10/0, no stim. Usually I focus more on tossing Guard around for more protection, but since we had 3 healers on our team, I decided to see how much damage I could muster. I've hit 517k as 10/31/0 with Ion Cylinder, but forgot to take a screenie.
The ultimate point I'm trying to make is that PT tanks are perfectly viable in PvP, even in full Shieldtech PvE tanking spec. The key is tweaking your PvP gear to maximize DPS while not giving up too much "tankiness". You can argue semantics and specs all you want. In the end, the damage can be comparable to AP, but with the added benefit of using Guard and more survivability.