I think the 500kh version is vapourware. Have a read of this forum and you will see the users of the "supposed" 500kh sets are only getting 400kh at best. People see a screenshot of 10 units hashing near a 500kh range believe that this is the long-term stable speed. But in reality if I power cycle my units enough time and look at it the first few mins I would get such a reading from the interface. It is just an estimate for a few minutes.

~ 400kh is the best you can do at the moment without new development from the manufacturers. There will be small increases coming soon.