What affect does the number of holes in a shock piston have

The larger the hole, the quicker the pistion re-acts to initial load. The more hole area, lets more fluid pass as the piston moves after the initial movement. If you have one hole with a .1 square inch area, it will react faster to the initail movement. But it will pass the same amount of fliud as 5 holes with a total of .1 square inches. But the smaller five holes, will not re-act as fast.

Whats the best hpi piston to use for flat asfault?

Smooth or bumpy track?

Smooth