If you have bearing clearances that are on the race side,(.025 or more) I would stick with a good race 20x50 or race syn 15x50. Thump you drive on the street and do hammer it once in a while, so your oil will be warm and need the higher viscosity to protect the bearings.
Thats assuming you have the .025 or more clearance in the motor. Tighter than that and I would call the oil manufacturer for their recommendations. As a side note, the new Mustang Shelby engine requires a 5w50. I am betting the wide spread is to accommodate tight bearing clearances for warm up and the high power level at running temps.