Originally posted by Comic Book Guy Vulcan would have a massive advantage, now being experienced with his energy powers. He can use that to manipulate Nate Grey's own, whose psionic power is arguably cosmic in its level.
Darwin and Sway's powers on paper turns this thing around. However, I don't recall Vulcan ever manage to effectively use them offensively (I could be wrong, so please check Deadly Genesis). Sway's powers kept bringing back visions of the past and Darwin's powers kept Petra and Sway's powers together and active in Vulcan's body. Theoretically, the nature of Darwin could prevent Nate Grey from defeating Vulcan (due to the seemingly limitless extent of his power). But, as we all saw from WWH: X-Men, Darwin CAN be overcome, and would be teleported away from battle.
Shaman X-Man is Nate Grey with a mental maturity about his powers. He's still as powerful as ever, but he uses it more ruthlessly now. His telekinetic powers has a broader application than energy-manipulation -- he can move large objects to dimensional barriers to molecules. There's also his vast telepathic powers to consider too, which Vulcan doesn't really have a defense for, I believe. But remember, his body is still stressed under all that power, and with overuse, can actually be destroyed by itself.
Off the bat, Nate Grey can mind-rip Vulcan.
Vulcan, on the other hand, can sense the immense power of Nate Grey. He can try to manipulate it to go nova, similar to what Gambit did to New Sun. Or he can try to override Nate's command, thanks to Vulcan's Omega-level energy-manipulation.
Nate Grey can also manipulate the biological functions of Vulcan's body with his TK. He can seriously mess with his brain chemistry, which can induce a variety of effects that can range from incapacitation, to seizures, to even loss of powers. Also, Nate can keep his distance while doing this.
Given the characters' personalities, I see Vulcan striking first while Nate Grey remains passive-aggressive, but attacking via TP. Hard to say who wins -- but if Rachel Grey and Nate Grey's battle would escalate to some "quantum reality battle" (according to an interview with one of the writers), then a Vulcan vs. Shaman X-Man battle would be comparable, if not be more intense than Vulcan vs. Black Bolt.