That is not an easy question to answer as it is all down to de-dupe.
Let me try and explian...
If you backup a 2TB server to your MSDP server on the primary site it will de-dupe some of that data itself.
If you could also backup the same server to the appliance that is due to be sent to the DR site then it will do the same - but will have all the same data and fingerprints as the live site appliance.
So next time you run the backup you would get pretty much 100% de-dupe on the primary site and as the dr site has the same set of fingerprints it would need to send a minimal amout of data across the link in order to replicate that 2TB backup - so a 56k modem may be enough!!
On the other hand your DR site appliance may be blank in which case the first AIR replication may need to send over 1TB across the link so you could do that calculation for yourself.. but the next backup that runs would not need to send much across as you now have a well seeded appliance at the DR site.
All very much down to whether you can seed the DR appliance first and what sort of de-dupe rates your are actually getting for your data as that will have an effect too.
So encrypted Oracle files or video files that do not de-dupe will need a lot of bandwidth and time to replicate where as docs data etc with near 100% de-dupe will need very little
So the answer to your questions is pretty much that there is no answer!
Hope that all makes sense and helps - seed it first if possible and look at your de-dupe rates to answwer your own question
