apart from total drag, what I was taught when it came to race oils was that film strength was very important and how this related to imoproved ring seal. (and hence torque and HP)
Neo's claim in the early nineties with their low and ultra low viscosity oils made better torque, as well as HP right through the rev range and this was supposedly attributable to better film strength/ring seal. Dyno testing I did at the time seemed to bear this out.