Sorry, I don't do PVP, so no help. I would think dirge would be a little better, from my experience, but I have had Troubs tell me that they do just fine in the blue server contests.
What differences a red server would bring, I don't know.
As far as Duo for a dirge, I do Templar/Dirge. It has worked fine.....having said that, a Mystic or Fury ( have a 30 mystic and a 20 Fury) might be a better choice. I have a feeling the templars magic resist debuff might help the dirge's debuffs land a little better, but no real 'proof' other than it seems so in my experience. He also debuffs melee mitigation.
Heres the deal, dirges are avoidance tanks. Templar healing works 'best' if the tank gets hit a lot for a little(reactive heals)...which is better for a mitigation tank (Guardian/Pally). Templars are plate wearers and can be used to pull and tank the mobs initial onslaught.
Mystics heal with runes (absorption heals--same limitation as templars?). However, they have disease based spells which complement with dirges strength in that area. Also, Mystic is a tad more active, with 2 or 3 debuffs to be cast against each mob (possibly causing aggro shift as well....which the mystic can handle nearly as well as the templar).
Furies have Heal over Time. I think this might be handiest for with a scout? Some of their offense is non-active...ie cast a Damage Shield...which is set and forget. Leather armor only, so you probably won't use them as part of a split damage or ping-pong strategy...at least as much. They also work on the disease side to complement the dirge.
I have done the 2-box thing with a dirge/fury or dirge/mystic, but if I were starting over, I 'might' choose a fury over a templar. Temps do debuff melee mitigation, which helps my dirge on that score. People build bards two ways, as a melee that does spell damage....focusing on ac, agility, strenght..which you kinda have to do if you tank him.....or as a caster that can melee...focusing on Int/agility for better spell damage and power pool. The latter feel they do more overall damage in groups (I disagree...i think its even) but certainly the bigger power pool is helpful on the big fights.