Our group all owned 530 hcx's for the last 8+ years and over the last 3 or 4 have migrated to the 650's as our older units have failed.
The 650's pale in comparison to the 530's as far as polling, sending waypoints, ect... The radio reception seems almost comparable, but the data sending capability is poor on the 650's. The GPS reception seems about the same and the screen is a little better.
We all wish the 530's were still available. I currently own a 650 and a working 530. We're waiting to see how the 700 series works out before we spend the coin to get out of the 650's.
Paid around $500 for the 530's and maybe $350 for the 650's. I'm guessing the drop in price wasn't because they figured out how to produce a better product at a lower price point.
If you get or have a 650 and you haven't updated the software you should. They constantly release updates that fix little quirky things, and unfortunately tend to cause other little quirky things.