Only the UD4P supports SLI although its performance in Crysis is disappointing - it's two frames per second slower than the Asus and just slightly slower than the MSI, despite the fact it has two full PCI-Express 2.0 x16 lanes like the other boards.
The performance in Far Cry 2 is a little better for the UD4P here as it stretches a lead in average frame rate over the MSI, but loses by an almost equal quantity to the Asus. The minimum frame rates are all consistent though.