Out of curiosity are there any special priority moves?
The following is a list of all moves with +1 or greater priority (damage moves are in bold, with their BP). Gale Wings makes any Flying-type moves get 1 added to its priority and Prankster adds 1 to the priority of all status moves.
+7:
Pursuit (40) (only if target is switching out on the same turn in which case the damage is double (not double BP, there is a difference because of Technician), otherwise has +0 priority and regular damage)
+5: Helping Hand
+4: Detect, Protect, Spiky Shield, Magic Coat, Snatch
+3: King's Shield, Endure, Quick Guard, Wide Guard, Crafty Shield,
Fake Out (40)
+2:
Extreme Speed (80),
Feint (30), Rage Powder, Follow Me
+1: Ally Switch, Baby-Doll Eyes, Ion Deluge,
Bide (--), Aqua Jet (40), Bullet Punch (40), Ice Shard (40), Mach Punch (40), Quick Attack (40), Shadow Sneak (40), Water Shuriken (15, 2-5 hits), Vacuum Wave (40)
The only special damage-dealing priority move is Vacuum Wave. The only fully-evolved pokemon that can legally have it in X/Y are Hitmonchan (level 26 or egg move), Scizor (relearn as Scyther), Hitmonlee (egg move), Hitmontop (egg move), Lucario (egg move), Toxicroack (egg move). The following fully-evolved pokemon can learn it via move tutor in Platinum and HG/SS: Primeape, Poliwrath, Machamp, Hitmonlee, Hitmonchan, Hitmontop, Mew, Heracross, Blaziken, Breloom, Hariyama, Medicham, Infernape, Lucario, Toxicroak, Gallade.
Of all those pokemon, I am fairly certain the only ones viable with a special or mixed set are Lucario and Mew. Medicham and Toxicroak have SAtk base stats that are comparable (but still smaller than) than their Atk base stats, but they are still played mostly with physical sets. All the others should be played only as physical.