PCIe 3.0 x8 card in PCIe 2.0 x16 slot: will it run in PCIe 2.0 x8 or x16 mode? - PCIe+graphics+2.0+3

I've seen a number of questions asking similar questions to the above, but I couldn't see that anyone had asked my specific question yet, so here goes. I'm about to buy a Gigabyte GV-R725O5-2GI PCIe 3.0 x8 video card. My motherboard has PCIe 2.0 x16 slots

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