I've got the Lumia 640, so same innards and screen res, but lesser camera. I'm running 10586.29 on it currently and for the most part its very good. Some bugs here and there, from the message boards on this site it looks like that is still the issue in some cases, so I haven't rushed to upgrade to the newer builds. Overall, very snappy. I have a Lumia 920, which has a high end processor for 2012, I find the performance between the two of them to be roughly identical for most tasks. I've been using Windows 10 Mobile as my daily driver since .29 came out and it hasn't left me regretting that decision.