The spacing should be 2-3 slots apart on all boards (you can send your thanks to 3DLabs on that one) and the NV Silencer 5 doesn’t take up any more real estate on the card itself from the VPU forward than the stock cooling does (it obviously takes up quite a bit of space behind it due to the large fan), so it should work just fine if the golden fingers are not further more than an inch or so further from the mounting bracket than the VPU is. This does include the EN6800, however unfortunately Asus does not follow standard fan plug design for their graphics cards so to use the NV Silencer 5 you will need to mod it a bit or hook it up directly to the PSU (Arctic cooling has instructions).
You will therefore have to pick your cards carefully for golden finger position. Fortunately, when ATi’s SLI launches ~Q2 it will not use any bridge, it will rely on manufacturers meeting the PCI-E specification for high speed switching between cards. Looks like Via’s up a creek without a paddle … (nVidia’s chipsets are not in that much better shape either, but at least they will support two ATi cards correctly, although Intel chipsets will support three or more in SLI).