As i know that upcoming cpu's of intel ivy bridge support fully pci-e 3.0 speed. But what about the current sandy bridge does they are good for the new gpu's like hd 7970 or 7950 can it run on it's native performance on 2500k or 2700k where i see that those cpu's support only pci 2.0...
The 7970 and 7950 will run at their full speed on PCI-E 2.0, they only use about half of PCI-E 2.0 bandwidth, you don't need to have PCI-E 3.0. If you run them in Crossfire in x8 x8 mode, you may lose a small amount of performance with 2.0, though the performance hit would be quite small, only a couple of frames per second in most cases. In short, no you do not need to wait for Ivy Bridge to get the full potential of the 7970 or 7950.
It's going to run OK with very minimum level of loss of performance when you run a 3.0 card in a 2.0 slot. Even with crossfire 8x/8x you will probably see a very small difference. In my prediction staying Sandy Bridge is going to be good until Haswell (skip Ivy Bridge). They are labeled PCI-E 3.0 because it uses the latest technology which is backward compatible with PCI-E 2.0 without big or noticeable loss of performance.
The 7000 series is meerely the first card to conform to PCIe 3.0 specifications, but that doesn't mean it can use all that bandwidth. On top of that PCIe specs that they must always be backwards compatible.
A full 16 lanes of PCIe 2.0 (or 2.1) will not in any way hinder performance. At 8x you might see as high as 5% loss, which translates to a couple of FPS avg.
Eventually cards will come out that will need more bandwidth than PCI-e 2.0 slot can provide. Similar to PCI-e 1.x slots; I think a single Radeon HD 6950 / HD 6970 may be bottlenecked by a PCI-e 1.x slot.
I apologize if I'm being redundant, but I'd like to chime in and explain what a PCI-e revision really is, and what it means to a builder.
As you know, cards are labeled with a PCI-e version number they are designed for. This is not actually a requirement, and in fact basically all PCI-e devices are compatible. You can put a 3.0 card in a 1.0 slot, and a 1.0 card in a 3.0 slot. The card will run at the maximum speed it can, and that the slot supports.
So, if everything is compatible, why have different versions at all? The answer is simple. Bandwidth.
PCI-e 1.0 supported 2.5 gigatransfers per second, or 2.5 GT/s, per lane. So, a PCI-e 1.0 card on an x16 lane would be capable of 2.5 x 16 GT/s (40 GT/s).
That's a ton of bandwidth, but progress marches on and newer cards needed more, so we get PCI-e 2.0, which doubled the bandwidth per lane to 5 GT/s. Lucky for us, the PCI-e Special Interest Group is ahead of the game, and are ratifying new standards before we actually max out the previous one.
So, when PCI-e 2.0 came out, we weren't maxing out 1.0 yet. But, because everything is compatible with everything, motherboard manufacturers could start using the new specification without caring when users would upgrade. The hardware would just work. It's the same story with 3.0. We get the wiggle room before we need it.
So, for a user, the PCI-e version number just provides more upgradeability. You can drop a 3.0 card in a 2.0 slot, and get effectively 100% of its performance potential. In a couple years, though, the 2.0 spec will probably be too slow for 3.0 cards, so you'll get throttled. Similarly, if you cram a top end 2.0 card in a 1.0 motherboard, it will work, but you'll be throttled.
Wow, this is going to be a problem for me. I've just found out that my GA-P35-DS3L Gigabyte motherboard is only PCIe 1.0. I am kinda dissapointed in finding this out, because I was excited to get a new HD 7770 stating it has PCIe 3.0. Does the performance of a 3.0 card decline very rapidly when with a 1.0 slot? I read that sometimes the performance declines even more if you have crossfire or sli in this specific configuration...
Oh, that's good news then. I haven't done too much research on the bandwidth of the two different slots and how they work with the two cards though. I was originally going to purchase the HD 6950 a while back, but since i'm the type of person that doesn't go hardcore with gaming I changed my decision. For what I do, my PCIe 1.0 motherboard does the trick