Accelerate x264 1st pass?

[Marsu42]

Since H264 encodes take quite a while, there seems to be the possibility to drop some calculations for the first pass. In combination with a simpified avisynth script for this pass, this should be able to save quite a lot of time. However, I didn't find anything conclusive on this matter, everyone seems to have his/her own opinion on which options are how negligible...

I guess parameters like ratecontrol need to be kept constant throughout the passes. That leaves some of the analysis and one frame type option(s) open for discussion:

--ref
--analyse
--8x8dct
--me/--merange
--no-chroma-me
--subme

What danger is there if I'd e.g. use
--ref 1 --analyse none --me dia --no-chroma-me --subme 1
for the first pass and
--ref 5 --analyse all --8x8dct --me hex --subme 6
for the second=last pass?

Does it have any important impact on the stats file if I use a different --merange w/ --me umh?

I certainly could run all combinations for myself and look at the stats file and encoded video, but maybe someone has tried these out already?

Edit: I am aware that there are the MeGUI "turbo" and VfW "fast first pass" options. But other tools like x264cliGUI let you choose for yourself, and sex264 recommends just dropping p4x4mv and b8x8mv, reducing the # of reference frames only by half and adjusting the subpixel refinement to no lower than 3. I am therefore wondering what difference which switch makes and if e.g. dropping --8x8dct like in the example above is possible, too.