Does PCIe 2 GPU force all PCIe slots to use 2?

[Sansari]

AFAIK, you have to have all PCIe 3 parts to use PCIe 3 bandwidth, including the CPU, motherboard's pci slots, and GPU. My question is, if I had a mobo with several PCIe 3 slots, and I used a PCIe 2 GPU, would it force all of the PCIe slots to use vers. 2, or just the one slot? Does it depend on the motherboard?


More info if you're interested:

Right now I've got a gtx 275 and a phenom ii x4 in a mobo with two PCIe 2 slots (x16 x4). I plan to get a gtx 670 (or 660Ti, 680?) now, so the 670 gets PCIe 2 x16 and the 275 gets PCIe 2 x4, which likely won't raise a bandwidth issue. I'm thinking of getting a Haswell or Broadwell board in the future, and eventually a gtx... 800? series card.

SO, my concern is if I plug in the 275 into that new board, will it force all the PCIe 3 slots to run at PCIe 2, or will the 275 get PCIe 2 and the newer cards get PCIe 3?

I know PCI bandwidth is never seen as an issue, and I've seen articles here and on other sites that state this fact, but
1: I've heard GPGPU purposes are the one case where PCI bandwidth can actually bottleneck cards (though I don't know if this is true, verification please?), and I plan to do CUDA and OpenCL based raytrace rendering on all of the cards
2: it's likely that the future cards like 800 or 900 series will require more than the max PCIe 2 bandwidth

So yeah

 

[Forceman]

No, the PCIe 2.0 card would run at 2.0, but the 3.0 card can still run at 3.0