recent models of motherboard with the intel x99 are now offering up to 18 SATA ports, this is nice for having a lot of hard disks, but my current chassis has room for 4 disks.
i may move into the larger 750D which has 6 bays with some smaller bays for SSD drives, the thinking is more room for my cpu cooler etc
so a realistic number of SATA ports seems to be more like 12 as being plenty.
rather have lots of bandwidth and fewer SATA ports with the next gen SB
my current board has the SB950 southbridge which offers enough for my mid tower with 4 disks and one for the optical drive
pci express speed is not such a big deal unless memory bandwidth improves
that speed is more useful for a raid card or a network adapter
my board is x16 x16 which is what i like only for the reason that the card(s) will not be bottlenecked easily
corsair has an even larger chassis, the 900D which is even more insane
no need for that big of box, the 750D is plenty, its already EATX