What's the bandwidth between two VMs on the same host

I have two Virtualbox VMs, the network configuration of one is NAT and the other one is NAT+host-only adapter.My host is a desktop located in a university lab with Local Area Coection 100.0 Mbps, Realtek PCIe GBE Family Controller #2.

Could anyone please tell me when I transfer files between these two VMs, does the traffic go through LAN or not?

The Linux command iperf gave me around 180-300Mbps bandwidth between these two VMs in a 10-second interval. Does this mean the maximum available bandwidth between two VMs are about this much?

Thanks very much!