HD650 are very smooth sounding and good for things like acoustic music or vocals, also very good for films and games. They are not brilliant for electronic music or pretty much any music other than slow acoustic or vocal type music really because they are quite slow sounding and do not have any sub bass at all. They are good headphones but I would personally not say they are all rounders as they are only excellent with some genres and not amazing with others due to the slightly dull sound, if you want them to relax to classical music or watch films then they are awesome but for faster genres or electronic music they are not so good.
Have not actually heard the HE500 but I am pretty sure that they would be a big step up from the HD650 from what I have read in terms of speed, sub bass and exciting sounding. Also the HE500 are 2.5x the price of the HD650.
Edited by nicholars - 11/30/12 at 10:18pm