Im buying a new motherboard to go with my i5 2500k Intel, and im trying to decide whether or not to get PCI 3.0. How does it work? If I go with PCI 3.0 will I have to buy a new graphics card to take full use of it, or will my dual nvidia GTX 275's benefit from it?
heard some speculation that AMD upcoming HD7k series might stick to PCI-E2.1 instead of PCI-E 3.0. for nvidia cards the low end / mid-range might stick with current PCI-E 2.0. only the high end ones will utilize PCI-E 3.0. but PCI-E 3.0 based gpu is not the only reason you go for PCI-E 3.0 mobo. if you run SLI/CFX x8/x8 with PCI-E 3.0 is the same as x16/x16 for PCI-E 2.0
PCI Express 3 doubles the bandwidth of the PCI Express slots, as compared to 2.1.
PCI Express 3 is backward compatible with 2.1, so your existing GTX 275s will continue to work in PCI Express 3 slots without any issues.
Go for a PCI Express 3 mobo, if you find one that's to your liking. The current crop of GPUs don't even saturate PCI Express 2.1, so going in for PCI Express 3 is more of future-proofing.
Since you've got an i5-2500k, the 1155 socket is good for Ivy Bridge, so you've got a bit of future-proofing there too (beyond that, who knows what Intel's up to).
Because the PCIe controller is integrated into the CPU.
However, Ivy Bridge will support PCIe 3, and OP's mobo for i2500k would allow moving to Ivy Bridge.
As I mentioned, its future proofing, so I've recommended PCIe 3 only if the rest of the mobo is to the OP's satisfaction. It needn't be a key decision point.
He's talking about bandwidth available to both cards. If you run SLI in an 8x/8x 3.0 board, it should have the same PCIe bandwidth available to it as if it was running 16x/16x in a 2.0 board. Won't make much of any difference right now, but in a 3+ years when we have faster video cards you might care.
If I'm not mistaken, most current socket 1155 motherboards will support PCI Express 3.0 if and when they are coupled with an Ivy Bridge processor.
However, that is for running one video card. If you want to run SLI or Crossfire, there are switches involved that are not PCI 3 ready in most cases. That is where a motherboard needs to be specifically rated to handle PCI 3.
The ASRock Z68 Extreme3 Gen3 is one of them for instance.