I think you will find that the fork meathod on that box will give you better performance than threading. If you have sole access to that box while this is running limit your fork to 4 proccess, any more and you will see diminishing returns as the cpus will need to csw on the uncompress proccesses. If you end up using gzip, you may want to look at a gnu version -- I have seen 20% speed ups from the vanilla Sun bin. You may also want to investigate the difference the different compress flags have on your files -- if these are dna tag files a small dict with low compression may buy you the same compress ratio (or close) with way less cpu time.