I'm working on a content synchronisation module for Drupal. There is a server module, which sits on ona website and exposes content via a web service. There is a also a client module, which sits on a different site and fetches and imports the content at regular intervals.

The server is created on Drupal 6. The client is created on Drupal 7. There is going to be a need for a Druapl 7 version of the server. And then there will be a need for a Drupal 8 version of both the client and the server once it is released next year.

I'm fairly new to git and source control, so I was wondering what is the best way to setup the git repositories? Would it be a case of having a separate repository for each instance, i.e:

Drupal 6 server = 1 repository
Drupal 6 client = 1 repository
Drupal 7 server = 1 repository
Drupal 7 client = 1 repository
etc 

Or would it make more sense to have one repository for the server and another for the client then create branches for each Drupal version?

Currently I have 2 repositories - one for the client and another for the server.