[Sephiroth]

The Hitron boots up and handshakes with the VM data centre in the same way as a residential hub. It receives a local IP address as a client of the "residential" host.
All subsequent tunnel traffic goes through that link.

When the link is established, the Hitron firmware sets up the GRE tunnel via the "residential" router at VM data centre, which then routes to a VMB server somewhere that does the rest of the tunnel allocation.

Once up and running, there shouldn't be a problem as it's all a matter of routing; encapsulation isn't a significant overhead. However, if your neighbours aren't getting good speeds, then there's likely to be congestion on the residential side. So it's worth talking to neighbours if you can.

EDIT: I forgot to mention to mention the MTU size. The residential MTU size is 1500 bytes and it'll no doubt be the same at the target end; the GRE tunnel requires 28 bytes overhead and so the data payload is 1476 bytes. This will lead to fragmentation. See Scenario 5 of https://www.cisco.com/c/en/us/suppor...frag.html#anc5 for full explanation.