Choosing a motherboard based on graphics cards

[prophet0001]

Hi,
Earlier in the week I was asking some questions about laptops and got some very good responses from you guys. Thank you for that.

However, I have since considered the possibility of foregoing the laptop in favor of a good desktop build.

The question that I have has to do with the purchasing of the proper motherboard to support the GPUs that I would like to run.

Basically, there are two platforms that I have in mind. The SB-e and the SB. I am wanting to run two 7970s in Crossfire on this motherboard but vaguely recall seeing that the 7970 can saturate the PCIe 2.0 bus. The SB has 2 PCI 2.0 x16 slots but can be only be used simultaneously in x8 mode. The SB-e is a bit more than I would like to get into but can provide at least full support for two 7970s with all of the bandwidth provided by the PCIe 3.0 slots.

I guess what I really would like to know is if two 7970s are going to be bottlenecked by the PCIe bus on the SB platform. If they are not then I have no problem running a z68 based motherboard. If they are then I'll have to upgrade to the x79.

Thank you again for your help.

 

[superjim]

http://www.overclock.net/t/1188376/hardwarecanucks-hd-7970-pci-e-3-0-vs-pci-e-2-0-comparison

"The results couldn’t be any clearer: the HD 7970 doesn’t benefit in any way from a PCI-E 3.0 link to the CPU. However there are a few caveats that should be mentioned. Even though a single HD 7970 may not saturate a PCI-E 2.0 x16 slot, things could change drastically once two of these cards are installed into a Z68 motherboard which uses a dual 8x setup for Crossfire and SLI."

I think PCI-E 2.0 x8/x8 should be ok for the time being. If not, get a PCI-E 3.0 x8/x8. There are other members on the forum with CF 7970s.

 

[prophet0001]

Thank you for your reply and that link Jim. The dual x8 saturation is in fact what I'm concerned about.