I'm going to be converting my sprinkler system from black polyethylene
piping to pvc. I thought I recalled hearing that one of the advantages
of pvc is that one diameter of piping is used throughout, usually
3/4", as opposed to the black poly that decreases in width the further
it gets from the pump. But an associate in a store told me today that
the same method is used for both: start out larger decrease as you
go.

There are 3 zones with 12 - 15 heads on each zone, with some in each
zone being 1/2 heads. The pump is 1 1/2 HP.

Will one approach yield better performance than the other?

Thanks.