I went from the Lumia 810 to the Blu Win HD... But I didn't care for many things on the HD (Like the volume on the left side and the new screen shot key combination meant I took 10 screen shots trying to power it on.... since it didn't have glance screen.
I mailed it back, went back to the 810, and am waiting for the 640. Though, 3 weeks ago, I dropped the 810 and shattered the screen.... so I'm getting impatient.