You have to get the same exact video card.
Sorry.
Oh, and both cards run on x8 PCIe Lanes.
One card is x16
Two is x8
Not sure how many lanes 3 cards get each.
And 4 cards is x4 for each card.
The reason is that mainstream CPUs still provide suppot for only x16 PCIe 3.0 lanes. (If I am correct, and it is very possible I am not)
However, even at x8 lanes, the bandwidth is wide enough for you not to have to worry about performance per card dropping.
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