According to this site, your disk is running 5900RPM. that is a tad faster than 5400RPM. But my logic tells me it should not differ more than 20-30 min. 1 hour tops. It could be my system is discontinued components from an old datacenter, (except the disks). I mean my SATA controllers are only SATAII, yet mb/s wise I should never hit the speed limit of that controller. But there may be instruction in SATAIII that could give a performance boost. But again I can get the math to fit with that big of a time difference. I guess I will see on Monday when the parity will run again if my cache drive will make a difference (just installed it today). I know it will not speed up the process, but I may spare some writes, and that should help on the time, but not much.
I save all my photos (I am a part time photograper) on this system, with backup to a local qnap, and also a backup to a long distance qnap. I use the parity to prevent bitrot, yes I know it is not meant for that. But then let us call it "off label use".