The wiki currently lists a 7970 with 650MHash/s at 1100MHz.

The 7950 has 87.5% of its Processing Units which equates to 568.75MHash/s at the same core clock (MHz).

Is this calculation valid?

I know from reading website reviews they reported the 7950 is not built as strong as the 7970 (pcb,fan).  That could be a factor in getting the same core clock.