We know that the Voodoo5 uses SLI for the dual chips, but what exactly is the bandwith between the two chips on a Voodoo5?

err, I don't think that there is any bandwidth between the two chips of a V5. Basically, each of the two chips produces every other line of a texture, then the texture is combined (somewhere) and displayed. I don't think there is any direct connection between the two vsa100s.