When making a submission with more than one card, it would be nice to have a "These cards are identical" or "These cards are different" checkbox. When you choose that they are different, a duplicate video card section would become available.
I say this because I've run multi-card benchmarks at different clocks and types of cooling. For instance, just yesterday I ran Vantage on two 5870s. One was watercooled and the other was air cooled. The water-cooled card also had higher clocks.