G5 taking aaaages on Compressor H264 encoding

i'm using a dual core 2.0Ghz G4, and have a bit of a problem - on Compressor, it seems to easily get to 9% (like, in under 10 seconds) when doing H264 encoding - Quicktime 7 400kbps for streaming..

.. and after this, it slows down and can sometimes say up to 55hrs to complete in Batch Monitor after finaly getting to 10% (which, from 9, can take up to two hours)...

i'm going to be wiping the machine, reinstalling everything, but is there any reason this could be happening?

(we're talking a 55min FCP film)

 

yeah i'm using FCS 5.1.

it's doing my nut in. i'll try QTPro, but it's really annoying that Compressor won't do it right.