Using Internal or External IP for File Transfers in Data Center?

I am pretty sure I know the answer to this, but 2 technical people in my organization cannot agree, so I'm putting this on ServerFault to get a final opinion.

We have a relatively simple set up in a data center:

• About 6 servers connected to an unmanaged Dell switch providing various web services.
• The Dell switch has the plug from our network provider.

We want to do file transfers between 2 servers to keep them in sync. Each server has an external IP and an internal one (ex: 192.168.0.5).

Is there an advantage to connecting the 2 servers doing the transfers using the internal IPs rather than the external ones?

From a network performance standpoint, if the public IP addresses are also on the same LAN as with the private address configuration (where all the systems are on the same subnet configuration(s)), then they are functionally equal in network routing/transport.

One slight advantage on the private IP plan side would be layer 3 separation from others "snooping" at layer 3, but that does not necessarily provide any protection at layer 2 (if it is compromised).

About 6 servers connected to an unmanaged Dell switch

Assuming both IPs are on the same interface, or they are on different interfaces, that connect to the same unmanaged switch, then there really is no difference.

I would be slightly concerned that there is no firewall/edge device between your systems and the network provider.