Haven't bought it yet, but probably a NH-U14S. I checked the pdf manual, I couldn't find anything that specifically that it'd run at full speed in any of the 3.0 slots. The specs page kind of implies it's only x16 in the first slot the way it's worded (PCIE1/PCIE2/PCIE4: single at x16 (PCIE1);)
See, they are making it way more complicated than they need to:
-
3 x PCI Express 3.0 x
16 Slots (PCIE1/PCIE2/PCIE4
- this says that all can run a single card at 16; but then it goes on to say:
-
single at x16 (PCIE1); dual at x8 (PCIE1) / x8 (PCIE4); triple at x8 (PCIE1) / x4 (PCIE2) / x4 (PCIE4))
- in which they are tying it to a specific slot.
So they are saying it both ways, but according to Intel, the slot is not a chipset limitation:
http://www.intel.com/content/www/us/en/chipsets/performance-chipsets/z97-chipset-diagram.html
as there are three PCI Express 3.0 lanes available in the chipset.
In contrast, my Asus board says "2 x PCIe 3.0/2.0 x16 (Single at x16, dual at x8/x8)," for the first two slots and "1 x PCIe 2.0 x16 (max at x4 mode, black)" for the third slot, which makes it more clear about how it handles these slots.
However, since both boards use the same chipset, the first two slots on the Asrock may be similar to my Asus, and they are just wording it differently.
BUT the Asrock gets even more fun if you are using M.2, which bumps
all lanes down to 8x.
Of course, as we've established, ASRock's Z97 Extreme6 is unique. It does have a two-lane M.2 PCI Express 2.0 slot competing for the PCH's limited bandwidth. But it also employs what ASRock calls Ultra M.2, which is a second slot tapping into a Haswell-based CPU's 16 lanes of third-gen PCIe, too. This slot isn't affected by the chipset. And if you drop a PCIe M.2 drive into the Ultra slot, you can still use SATA Express, which is wired into Z97. In exchange, you can't run a graphics card using the processor's 16 lanes, instead bumping it down to eight. Perhaps more severely, SLI and CrossFire configurations are out, too.
http://www.tomshardware.com/reviews/samsung-xp941-z97-pci-express,3826-3.html