With disk drives, AHCI is not so much about performance, but about SATA (like hotswapping.) With fast disks, there's a bit of a performance advantage with non-sequential reads due to NQC, but it's not much (it's limited compared to SCSI.) However, it also helps the drive's read head live longer as it travels less.
Note that SSDs don't have heads, so NQC is useless here. Access to the higher bandwidth however, is useful for fast SSDs.
I suppose this is a typical 5400 rpm HDD so it's kind of expected that it doesn't make much difference. Try the same thing with a fast SSD and see if the results are the same.
You've got it backwards. For slower drives, NCQ should help a lot, as heads won't have to seel as much. However, in my experience the difference is no noticeable.
For SSDs, NCQ means nothing.
Other AHCI improvements are not about speed (afaik).