The problem is some of the hashrates are incorrect.  

A 7970 will do 730 max..  a 7850 with half the shaders will do exactly half of that *MAX* (or 365).  And when I say max, I mean max.. a 7970 at 730 is extremely difficult to hit.

so while I don't have any 7870s, I can tell you 400 is practically impossible unless liquid nitrogen cooled.