Odd, the x8 cards I've seen before are for workstations.
Looking at them they both use a full length connector, all Gigabyte have done is to miss out half of the contacts, which is no problem.
So, finally, I will say that either of those cards will fit into a x16 PCI-e slot perfectly, work perfectly and there will be no loss of performance because the GT630 is not fast enough to demand a X16 link.
This bit is off topic so don't reply if you don't want to.
DDR3 memory is slow by current standards and the 64 bit memory bus is very narrow, as a gaming card it is going to be very weak. Of course if it's not for gaming it'll handle movie playback and general home uses perfectly well.