Fastest Encoding from a VOB?

You cannot use the first pass as the source for the second pass. The whole point of multipass encoding is you're encoding from the same source. Changing the source makes your stats file worthless. Reencoding an XviD file introduces another iDCT/DCT cycle which will further degrade quality, not to mention even the constant quantizer 2 file generated in the first pass does not retain all the quality of the original file. Don't do it - if you need the speed that badly, either dump it to huffyuv or just do it twice from the AVS.