Very nice discovery!
Too bad most of the non-SLI boards have only PCIe1x slots apart from the one PCIe 16x. Would it work even with 1x?

Onepagebook: Another thing, your 6600GT scores look weird to me as if the cards where running slow. Can you tell us how high the clock on those 6600GT was in 3D mode? I'm just curious to see if maybe the NVidia driver or your Bios did something to the clocks you set.
I'm asking because my single 6600GT does 4174 3Dmarks2005 at 579 core and 1150 mem (Nforce4-4x chipset).

Killeroy.