question about a Vdub performance option

[gatekeeper_007]

So far I'm using this option as default:
Options/Preference/AVI - Directly decode YCbCr(YUV) sources
and
Video/colorDepth: a) Decompression format (Autoselect), b) Output format to compressor (same as decompr. format).
and
XviD decorder's output format - No Force

My question is _ Would it be better if I disable this option in Vdub and enable the colourspace YV12 on XviD decorder, so the Xvid will handle it and output in YV12 format ?
and something else...
-what is the YUV420 format? because this is what I get when I recompress with "normal" or "full proce. mode".
Is "Fast recompress" in Vdub the only way to output YV12?

:stupid:
Thanx 4 ur time

[gatekeeper_007]

...well can anyone at least tell me if "YUV420" is the "I420"?
because if it is then:
YV12_is_ 8 bit Y plane followed by 8 bit 2x2 subsampled V and U planes.
I420_is_8 bit Y plane followed by 8 bit 2x2 subsampled U and V planes.
~These formats are very similar if I can't say identical, the only difference is the U and V plane order which is reversed.

Thanx anyway.