Been running my Lumia 640 (R2595 from Orange) for 3 weeks now.
It's a brilliant piece of kit and the dual sim and LTE is really sweet.
This phone is fast for it's spec and the operating system control you have over apps and resources is very welcome indeed. I go nuts swiping etc, and there is not a hint of lag or stutter.
Battery life is mad, as I don't play games, so I only need to charge it every 3 days. My previous Sammy needed to be charged twice a day under the same workload.
Plus you get a year subscription to Office 365 and 1terrabyte storage on OneDrive. Amazing.
For 2 and a half grand, this phone has a lot of my mates now seriously looking at MS phones or Non-Sammy phones running Windows 8.1 phone OS.