Dual Core transcode node 2 times faster than Quadcore Master

Hi!
I've encountered a very strange behaviour on my Cluster setup.

I've got a quadcore Phenom II and a dualcore Athlon II both running at 3
GHz, both ubuntu 9.04 64-bit with the standard ubuntu packages (only
dvd::rip is Version 0.98.10 - but only installed on the master - the
Phenom), I'll add a list of the package-versions at the end of the post.

The quadcore does a very neat job when transcoding sound and during the
first pass of xvid. I'm having 3 nodes running on it with each reaching
about 50-60 fps in the first pass. (1 node reached about 70, 2 also
about 70 but the system was at about 70% across all cpus. I thought this
was due to xvid (possibly not enough parallelization in it?) so I tried
to add one node more with a rating of 20). I use the very slow
deinterlacing method (zoom to fullscreen) and got about 6-8 fps on the
second pass. I didn't really mind - I decided to have slow (but
hopefully better) deinterlacing after all.

Today I added a cluster node - my mediacenter Athlon II and was a bit
stunned: While the first pass was about as fast as on the Phenom (in
fact a little faster but that didn't suprise me, it wasn't runnning more
than one node after all), the second pass reached about 40-50 fps!

My dualcore encodes about 2/3 faster, when getting it's data over the
network, than my Quadcore ... any ideas?
(btw. the problem only occurs when using xvid with the slow
deinterlacer, I'm quite sure that my quadcore isn't broken, in other
progs like avidemux or with x264 it uses it's 4 * 3 GHz)

I would like to know, if I'm just too stupid to get dvd::rip running
properly on my PC or if there is really some issue with using this
deinterlacer on Phenoms.

Packages:
  Programm             Version   
  -------------------------------
  dvd::rip             0.98.10   
  transcode            1.0.7     
  ImageMagick          6.4.5     
  ffmpeg               0.5-svn17737+3:0.svn20090303-1ubuntu6,
  xvid4conf            1.12      
  subtitle2pgm         0.3       
  lsdvd                0.16      
  rar                  3.80      
  mplayer              1.0       
  ogmtools             1.5       
  dvdxchap             1.5       
  mjpegtools           1.9.0     
  xine                 0.99.6    
  fping                2.4       
  hal                  0.5.12    
  -------------------------------


PS - don't need subs so I don't think rar is an issue

thanks for ideas!