2.5.x is Python 2.6+ (2.0 is the last one to support Python 2.5). The reason I'm not mentioning Python 2.6 here is just to encourage people to try to get onto Python 2.7.

Thanks.  To that end any chance of putting together a migration guide for Review Board (or is there one that I've missed)?  I've already given the IT guys at my office a heads up that Python 2.7 will be required soon, and they are probably going to move us to a whole new OS to simplify meeting that requirement.  But, they are already asking questions about migrating settings, data, etc.

I'd love to say "Sure, let me add that to my docs task list," and I will add it. Whether that'll happen during this batch of docs before something swoops in and takes up my time for the next few weeks, who can say.
Mini guide:

Get a new mod_wsgi on there that uses Python 2.7.
Switch pip and easy_install to use Python 2.7 (or invoke the -2.7 versions of those).
Install Review Board again, using the 2.7 version of pip or easy_install.
Sanity-check that rb-site invokes Python 2.7 (you can check the first line of the file).
Run rb-site upgrade.
Restart Apache.

That should basically be it. It's just about switching the tooling and getting the 2.7 equivalent of the packages on there.