[Johnnyas]

Thanks for the speedy help! I included the distributor line just because it said 'this line may or may not be necessary' in the first example script I used when trying out the MT version. I removed it now!

I tried removing the old 2.5 version to see if I could get any more speed out of 2.6, so the versions I've been using are:
AviSynth: 32bit 2.6.0 Alpha 4 [130114]
SEt's AviSynth 2.6 MT mod from 20130309
QTGMC 3.33 (because I had problems using 3.32, I tried 3.33)
QTGMC 32-bit Plugins [Vit-Mod].zip - Note: I tried using QTGMC 32-bit Plugins [Vit-2.6] as well, but I got an error with MT_Masktools (access violation in mt_masktools-26.dll), so I tried this package

MediaInfo:
General
Format : AVI
Format/Info : Audio Video Interleave
Format profile : OpenDML
File size : 131 GiB
Duration : 1h 29mn
Overall bit rate : 210 Mbps
TCOD : 0
TCDO : 53547200000

Video
ID : 0
Format : Lagarith
Codec ID : LAGS
Duration : 1h 29mn
Bit rate : 210 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 25.000 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Bits/(Pixel*Frame) : 4.051
Stream size : 131 GiB (100%)

I tried modifying the script a bit, just removing the distributor line and reducing maxmem, but that didn't seem to help much. When I checked in after ~5 hours or so, it was down to around 0,76fps. I didn't see neither much swap file usage, nor a lot of evidence of excess threading - at least not from what I could see in Process Explorer.

Separating the qtgmc and the x264 process seems like a good idea, guess I'll do some research on how to do that I guess. I've been using MeGui, and I'm not very familiar with virtualdub, but I guess now is a good a time to learn as any.

edit: oh right, should also give ffvideosource a go.