If you are plotting to multiple SATA HDD, on a capable system, with plenty of RAM, and still experiencing unexplained bottlenecks, I recommend you install a ubuntu Virtual Box.
Create a 320gb fixed VDI on each drive, ensure the VDI is located at the start of the disk - empty the disk before creating, and use defraggler to ensure the blocks are at the start (lightly fragmented is ok).
I am getting more performance from 4 parallel jobs on a 16gb 4core virtual ubuntu machine than I got from the physical windows 32gb 8core machine. (more cores can be granted to the VM of course.)
The disks are ACTUALLY getting utilised. What a wonderful sight.