Lots of comparisons in this thread. The 630 is end-of-life and won't be getting new feature updates (not enough memory).
Thanks for the infoThe 830 takes away some outputs, the clock and other indicators, it does have some enhancements for searching for things in the guide and programming. There are trade offs but if you 630 is still functioning I would probably stick with it. Had the 830 not removed the outputs and clock etc I would probably would change my mind.