greater than 100% scaling is due to margin of error combination for both single card and dual card tests in the vast majority of cases.

we also tested single card performance on an nvidia system and crossfire performance on an intel system, so the different computers will also add margin of error.

two card solutions generally don't scale at greater than 100% except in extraordinarily odd situations (where rebalancing loads might help with scaling on both individual cards -- but that's odd and rare).
that was posted by Derek Wilson, an editor on Anandtech about the scaling