Same here.

I hate lowering quality for speed, and unfortunately that results in week-long renders...  :-/

My only solution to speed Poser up, except from using the latest CPU and 2 GB of RAM, is to raise the bucket (chunk Poser calculates at a time) as high as possible. It's maximum size depends on memory requirements (scene complexity, textures, available RAM), and memory management isn't Poser's best side either...
Why raising the bucket? Poser seems to do calculations between each bucketfull, so less buckets you have, the faster it will render (check it on a simple scene). Adaptative bucket is your friend here, it allows you to start with a 512 bucket, and let Poser scale it down if at some point it chokes on memory issues (you'll see the bucket squares get smaller all of a sudden).

If despite the adaptative bucket you get the dreaded "no memory" message, it means Poser reached the bucket =32 limit, and even that wasn't small enough. In this case you can forget about speed and start using very low buckets (16, 8) hoping Poser will be able to gnaw itself though the scene. It will take ages though.  :-(

Note: Despite a quite popular legend, bucket size does not influence render quality. It's just the size of the chunk of picture Poser will load and calculate at once (since it isn't able to load the whole scene).