PgBackRest Ideal N/W need to provisioned ?

List,

I am doing a full backup using PgBackRest from a production server to
Reposerver.

My connection is IPSec VPN over ILL ( 8 Mbps link) between the
Production DB Server and the remote RepoServer.

I understood the bottleneck of 8 Mbps between servers. (Server NICs 10Gbps
and switch 10G)

The current size of the production DB data dir 500GB can grow upto 1
TB to 2 TBs during a time span of one year from today.

Query : I have started the backup command and it is running (may go for
hours and days as link speed is minimal, right now it is achieved only
25GB/500 GB copied from 10:55 Hrs to 22:00 Hrs) .

What should be the ideal connectivity without over provisioning the
bandwidth, but doing a full backup must finish within acceptable time
duration.

I mean the connectivity btw. production server to Repo server
i) ILL with SSL VPN btw servers
ii) OR MPLS between servers ?
iii) what should be the ideal bandwidth required considering the data dir
size mentioned above to do a reasonable backup (Full). within a reasonable
time window
iv) without over provisioning and underprovisioning what should be the
ideal connectivity and its bandwidth requirement to avoid network errors
and intermittent disconnection of links if any?

v ) Need to perform at least one full backup in a week

Any suggestions much appreciated

Thank you ,
Krishane