... The fact that it worked at all with the Pi Zero was surprising let alone at the same speed.
The Pi's seem to prefer a wired connection for best performance from my experience. I think the Pi's wireless component shares some of the resources as the USB ports also. My two R808's maxed out a Pi 3 so additional 2Pacs were run on a separate Pi 3. The Pi 3+ never exceeds 12% resource utilization in Raspbian with the 12 NewPac's.
Someone here might have better insight into how the Pi handles resources. I am going to try three GS hubs and 18 NewPacs on the 3+ but have another Pi should the USB ports be overwhelmed. A/B enabled should allow it to work, fingers crossed.