You guys & gals are overthinking this a little bit. Assuming the intended lubrication is present, the majority of friction will be due to sliding between the ball bearings that are taking the instantaneous load, and the races of the cone and the hub. Sliding is unavoidable because a monolithic ball bearing rotates at a given rate, while the range of line contact between the balls and the races require a variable rotation rate of the ball bearing. Of course, any non-circular irregularity in the bearings or the races will add to the friction, but that is mostly independent of the number for balls.
In the first approximation, sharing this sliding friction among more or fewer ball bearings will not appreciably change the net friction. It seems to me, that the main advantage of more ball bearings is increasing their longevity and that of the races, due to reduced cumulative fatigue damage (since the load is shared over more net contact area).