NEED? I read that PCI-E 3.0 cards will be fully backwards compatible with 2.0 slots.
If the AMD 6990 isn't even saturating a 2.0 x16 slot, and allegedly the AMD 7970 is equivalent in performance to the 6990, then the 7970 shouldn't have a problem on the 2.0 slot. Unless AMD or Nvidia just completely exceeds our expectations.
yes, PCI-E 3.0 is backwards compatible as a result loss of performance but it would be fine on PCI-E 2.1.
the more better way is get gen3 boards which has PCI-E 3.0 so if you want to run a card with 2.0 or 2.1 they will be fine.
Do you think a 2500K (even at stock clocks) will bottleneck a high-end single GPU 7000/Kepler?
For benchmarks, when you are hitting 200+fps it might be bottleneck but for gaming at 60fps I don't think so. Sure, there are games that due specific nature (civ 5) or outdated engine (skyrim) are CPU bound, but other games run just fine.
The reason is that the game developers want to have target audience as large as possible meaning that they want the game to run even with low end hardware. While graphics processing scales very well (you can reduce resolution and AA to get higher frame rates) the general processing does not. The developers have to optimize and tweak the system until it works well on most processors out there, including AMD processors. Since every i7 processor smokes anything amd has to offer you're in safe waters.
Sure you'll see 5..10% fps increase in games when you update the processor but it means that most of the time the CPU is waiting for GPU function to complete so it can feed in next command immediately. It does not mean that your current system is CPU limited but rather the update system is horribly limited by GPU. I'm still running my i7-920 at stock clock and plan to update to 2xGTX680 in SLI without worring a bit about the bottleneck.
i'm telling you sandy bridge cpu's are pretty faster and cannot be bottleneck the high-end gpu.if 2500k botleneck the latest gpu then think which cpu would be fine o handle 7000s or kepler only cpu is i7 3690x.