In a large pot of boiling, salted water, cook the pasta until al dente. Drain and rinse with cold water.
Meanwhile, in a large bowl, whisk together the mayonnaise, sour cream, lemon juice, cumin and 1/4 cup water. Add the pasta nd toss to coat; let sit for 10 minutes. Stir in the celery, bacon, chopped nectarines, half of the chives and half of the pecans.
To serve, top the pasta with the remaining chives, pecans and the sliced nectarine.