If all the captured video you have fits on to the 250, I would set up the 200 as the Conformed audio drive, and save projects to the 160. If there is room on the 200, you can certainly store some stills and even some DV video clips there too. If space is really at a premium, store the conformed audio files on the 160 and and dv footage on the other two. The secret is to have your captured DV footage on a seperate drive from the conformed audio files. That way when Premiere conforms audio, it does not need to read-write-read-write on a single drive. One drive is constantly reading, the other constantly writing – speeding up the process. Staying away from your system drive frees it up for windows tasks.
As for hyperthreading, as long as you have all the latest windows patches and adobe mainconcept 1.1 encoder update and the 1.5.1 premiere update, you should have smooth sailing all the way.
With the quadro FX, just have the latest version of the drivers.