Which one flows better, factory 6 blade water pump or 8 blade

AC cars have a smaller pulley, which spins the 6 blade water pump more turns per cycle. Using an AC pump for a HP build might be less drag, but at the expense of cooling. If you are going one quarter mile at a time, cooling is less of a factor.
I would stick with the way the factory designed the pumps in AC and Non AC cars.