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I know that this question may seem strange, but it's hard to find a clear answer anywhere.

I currently have the following configuration

Core i5 2500k (Sandy Bridge) 16GB DDR3 RAM 2 x Radeon HD 6970 Graphic Cards (in Crossfire) ASUS Sabertooth Z77 Motherboard

From what I understand, when using Crossfire, the two PCIE3.0 slots will only run at 8x. However, shouldn't that mean that the PCIE2.0 Cards should still run at 16x since essentially PCIE3.0 = 2x PCIE2.0's bandwidth?

I know that there is some limitations with the actual processor that I'm using. I've ordered an Ivy Bridge Core i7 and should arrive tomorrow. Once I upgrade the processor, will I still be in the same boat or will both Radeon HD 6970 cards be used to their full potentials?

If my goal is to run both cards at 16x, did I simply get the wrong motherboard? Gut told me to go with dual 16x/16x, but I wasn't sure if it was going to be an economically sound move.

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up vote 0 down vote accepted

A PCIe2.0 card will only run at PCIe2.0 even if you use a PCIe3.0 slot

Also, you need an Ivy Bridge processor to make use of PCIe3.0

Even though 3.0=2x2.0, thats on a per lane basis

The bandwidth wont be reallocated among more lanes like you are expecting it to be

Also, the performance difference is supposed to be minimal between 8x/8x and 16x/16x so I doubt you should be worried because of that

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I know that I wouldn't get the full potential of these PCIE3 lanes, but would I get the full potential of the cards when upgraded to an Ivy Bridge processor? – kobaltz May 3 '12 at 4:41
@kobaltz It is unlikely there will be any change in GPU performance when you get an Ivy Bridge processor, since the 6970 uses a PCIe 2 interface – Akash May 3 '12 at 4:44
Also, its a bit old, but see this… The difference is hardly 1-2% – Akash May 3 '12 at 4:45
Those were also lower end cards compared to a 6970. They may not have even pushed past 8x to begin with. – kobaltz May 3 '12 at 5:00
Basically what I'm comparing is running WoW on 5860x1080 in Ultra. I'm getting about 30 FPS with just one card installed at 16x and I'm still getting about 30 FPS with two cards installed, each at 8x. – kobaltz May 3 '12 at 5:01

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