A few days before I race, I imagine myself going away solo 2/3s into the race. As the race gets closer, I get a little more practical imagining a move on some corner or hill farther in. By race time, I'm usually only lighting my matches in the last kilometer, if I'm even contending.
The best tactic is to get to the finale with more left than the other guy: stay in his draft, keep the pace even, and do everything right (nutrition, hydration, ect.) along the way. If he is stronger than you, you have to force him to screw up one of those. The most easy is making him lead. Very rarely does out-foxing actually work mano-a-mano
I would sit on Wiggans's wheel, and let the journeymen/outside contenders go away. Sky/Wiggans will chase them eventually, if not in the early stages. Sky will weaken, Wiggans will work, and then nibali finds himself in a position where he has more left, then goes.
I always shake my head when I see guys fly and die in the name of "just going for it." Racing is simple, a lot simpler than people make it