I haven't seen any benchmarks that make it seem like Angular is "painfully slow." AFAIK, its on par or faster than ember.js and knockout.js. What would you use instead for MV* in the browser?
Our relatively simple Angular app was regularly consuming 100% CPU for literal minutes and ate up 600MB of RAM until we dramatically reduced not-actually-that-crazy number of API calls we made on load (from less than 100, mostly prefetching data – to less than 15, pr-fetching sacrificed). It is mostly related to Angular’s “dirty checking” and ajax management. I have met others with the same problem. (Their solution? Use Backbone!)
I haven't actually seen any decent benchmarks between those systems as a whole. Most comparisons seem to shy away from that (between some candidates it probably doesn't make sense to benchmark anyways). But if you've seen anything interesting on that front, I'd be thankful if you could post it. And, you're right, so far Angular hasn't let me down regarding speed.