Poor Linux software RAID 5 performance with NCQ

Thanks for updating the question! It seems like the NCQ test with the RAID5 is just exposing that the NCQ is done ignorantly of how the data must be written to the disks even if it is in software (this is a really common issue with IO schedulers and hardware raid in my experience, http://blog.nexcess.net/2010/11/07/changing-your-linux-io-scheduler/).

From: https://raid.wiki.kernel.org/index.php/Performance

NCQ of the controller can interfere with the Linux kernel optimizations

I think the other tests do confirm that NCQ is working when talking directly to the disk, as they either show a performance boost or are near as makes no difference to the noNCQ tests.

Regarding the 57s value it is just an artifact of how much IO buffer you have and the scehduler you are using. If you are concerned about interactive responsiveness of the IO system you should probably investigate a different scehduler (see: http://blog.nexcess.net/2010/11/07/changing-your-linux-io-scheduler/).