I was also curious on what Video filter process-ahead did, so I did a search and found some relevant information over at the
German doom9.
I used google translate and this is my interpretation.
Video filter process-ahead:
These settings
only apply to VirtualDub's native filters. If VirtualDub is set to "Video: Fast recompress" than the video filter process-ahead settings are simply ignored.
I agree with Keiyakusha, use
flash3kyuu.
I'm also using Avisynth 2.6 MT which does make a difference, even on my old beat up 4-core.