All CRMs I've tried make me waste time. Every single one feels like a web page from the 1990s, not like a web app. Round trips to the server are common.
What ideas do you have for one page app? Or rather what are you expecting?
well, something that I can operate entirely with the keyboard would be good. Something that doesn't introduce 2-3 seconds delay between operations, due to page reloads.
For an example of the latter: http://moviepilot.com/