Network capacity is usually the limiting factor in how fast the imaging will run. But it’s usually taken as something we just have to live with, it’s difficult to configure around it. Usually the most we can do is to distribute more OSD Bare Metal Server/Relays to get closer to the client network-wise, but often there are complications at the DHCP configuration to adding more of them.
Often the limitation over which you have more control is in the storage on the OSD server. Ideally it should have enough disk space to cache your OS images, and those can get pretty large so I usually recommend a terrabyte depending on your image count & sizes.