Re: Internal SATA cable speed
Current rotational based hard drives (vs SSD's) can't really saturate a SATA connection, no. And since SATA is point to point, i.e. one drive per cable = one drive per channel, that 1.5 speed is dedicated for each drive.
SSD's are a little more hazy though - even "general performance" SSDs can quickly saturate a SATA 1.5 controller, so at a minimum, for best performance, I'd have a SATA 3 capable board.