I've been playing with the talent calculator and I've linked my proposed build for PvP shadow priests at 85. Note than I plan to heavily rely on holy nova when the shit hits the fan, so instant spell mana cost reduction is a key. Also, I don't really plan on using vampiric touch that much since it has a cast time and if I'm standing there casting then I'll likely be nuking with mind spike/mind blast combos. I'm using the talent mostly for the mana regen. I've excluded evang/archangel because if the fight is lasting long enough that my shadow fiend, dispersion, and SWD regen aren't enough mana, then I'm dead anyway. I don't plan on casting mind flay so evang won't be useful.

http://wowtal.com/#k=Y-7C8tE8.a6d.priest.qzsq6E