Unless we get a large number of developers to build the same application twice using each framework, all evidence related to this is going to be speculative or anecdotal at best. Having written a lot of both backbone and angular, I can confidently say that I am _much_ more productive with angular, so much that I get incredibly frustrated and resentful when I have to work on a backbone project. I think if you do a little bit of research you'll find a sizeable amount of similar testimony from people who have switched from backbone to a more comprehensive framework.

Once you start supporting persistence and keeping things reliably in sync, things start to get very complicated. You'd still have to write that out in Backbone, when ember or angular provide it out of the box.