In theory more drives is more speed but most of the time it's a fool's errand because the NAS's connection speed is a fraction of even a single SATA drive.
But you will encounter folk that will not think about that and feed the makers of such gear.
I'm building a NAS server and was wondering would my RAID config have a faster read/write speed with larger 1TB drives x4 orr smaller 500GB x6 ?? Basically is it faster to have more smaller ones or fewer larger ones?