In a very large skillet, heat the olive oil until just smoking. Add the garlic and cayenne chile and cook until softened, about 30 seconds; do not brown the garlic. Add the wine and bring to a boil, then add the shrimp and cook until just pink and curled; if using crab, cook just until warmed through. Remove from the heat. Add the butter, lemon juice and parsley and season with salt and pepper.