Performance Debugging Recommendations

I have noticed many reports that a well-stocked 5D over Thunderbolt is able to get over 250MB/s for both read and write using the BlackMagic disk test on a Mac.

I have a 5D with 5 3TB WD RED drives hooked up to a new MacPro. I’m only storing just under 3TB (so 25% full). When I run BlackMagic disk test, I am only getting about 150MB/s read and write. I have a Crucial 128G mSATA SSD and have run the test both with and without the card installed: no difference.

I’m interested in trying to see what it will take to bump performance over at least 200MB/s. Any recommendations on how to proceed?