No this doesn't matter at all so don't bother doing so.

If it was the case, it wasn't the cable but the chipset of the board limiting it.

Does the drive's temperature sensor continue to work when you detach te sata power cable only?

Or does the de original hdd need sata power as well to provide the drive's temperature values to the iMac?

I'm asking because the drive is faulty and makes noise. I'm placing an ssd in the dvd bay area and don't want to use any software to control the fans.