Originally posted by xandros9
640 XL:
Larger size and display
8 GB internal memory
Superior front-facing camera
830:
Lower resolution but superior rear camera and camera button
Full-featured Glance
16 GB internal memory
Qi wireless charging
premium design
Both will perform largely the same, since they are powered by mostly the same internals. (1.2 GHz Quad-core Snapdragon 400 + 1 GB RAM)
Both have SD card slots
I would get the 830 because it's a better overall combination for me, having Qi and OIS as well as being smaller.