can bitrate determine encoding passes?

[needforspeed]

I'm encoding the movie Serenity using Divx 6.1.1 at a resolution of 512 x 368 with a video bitrate of 1314 kBit/s for a 2cd burn. I was just curious if a 2-pass encode would give me a significant increase in quality over a 1-pass encode at this bitrate? I have all ready encoded Serenity using a 1-pass encode and it looks good to me. I was just wanting some opinions before I took the time to set up a 2-pass encode. Also, is there a high enough bitrate where the quality of a 1-pass = 2-pass?

[CWR03]

Due to the nature of two-pass encodes, a two-pass encode will always be better than a single-pass, given the same bitrate (the two-pass would have to be an average bitrate equivalent to the single-pass). In order for a single-pass to equal a two-pass of the same bitrate, the end file would likely be bigger than the source.

[o770]

If you can find what value the quantizer averaged at during the encoding process then you may benefit from encoding the movie again in the Quality Based mode at that fixed Quantizer and achieve constant quality that you don't actually have, while keeping file size about the same (only because you already encoded the movie and found what value the quantizer averaged at). I beleive this would be your best bet at getting the highest quality encode to fit your file size need.
Or you may run 2-pass enc. instead at that average bitrate (1314) to benefit from what CWR03 has just described.

I would go for the first method only if I knew what quantizer value to set.