The ideal viscosity will be dependent on the bearing clearances in the engine and intended use of the engine. You will take the advice of the company building the engine, advice of your lubricant supplier, and past experience in making the decision.
Back in the days of qualifying specific engines, you would only run a 0W or 10W in the engine because it was only intended to run minimal laps. The 50W oil makes a lot of sense for an endurance application especially on a LS based engine. For something like NASCAR qualifying where you tape up the front of the car, you would also run the least amount of coolant necessary. Something also done in NASCAR especially in plate track qualifying is to take the belts off the engine. You don't need an alternator to run 2 laps, same with a water pump or power steering. The drivers will shut it off as soon as they cross the line and coast around without touching the brakes.