git - project evolution, branch or new repo?

I have developed a Google App Engine web application versioned on GitHub.

I'm going to "port" this application making it GAE agnostic; this port would have several files in commons with the original project but also a different file system structure.

Is it better to create a new branch (nogae) and work on it or is it preferable to create a new git repo (开发者_JAVA百科project.nogae)?

What's the pros and cons?

Arguments for two branches

Creating a new branch is interesting if the two versions are tightly linked together (some evolutions on one are likely to be reported on the other):
If the files are the same in both branches (even if their names/paths are different), a branch is a good choice.

Arguments for two projects

But if the two projects will evolves independently, with few common files, then two separate projects are better.
If the common set of files is important enough, then a third project might be created and imported in the first two ones as a submodule.