My father used Castrol R 10W - 60 for years in his 1993 HSV Clubsport 5.0L. He found the oil made the car feel a bit sluggish so recently, he changed to Castrol R 0W - 40 and he believes the car runs much better.
He doesn't drive the car hard so there should be no issue
No doubt the 10W - 60 is a premium oil though, just relatively high viscosity.