You may want to look at EmberJS[1] if you want a more opinionated framework for single-page apps. It's still in development and I'm not sure if all of the components are production-ready but I've also heard (??) you can use it alongside Backbone.js
I would be surprised and confused to see how one would use Ember alongside Backbone. Both Ember and Backbone have separate notions of how models should be handled as well as having separate routing systems.
I'm not entirely clear what you'd be mixing and matching.
I have been following Ember since it was still SproutCore 2 and I am looking forward to try it out on a hobby project. Looks like they took the good parts of other frameworks as inspiration and left the bad parts of SproutCore behind, but a little too cutting edge to use in a project with real deadlines for now :P
[1] http://emberjs.com/