PCIE 2.0 x8 saturation

[blacken666]

Hey thf,
Been looking into doing a Xfire config with 2 6850's on a M4A78T-E mobo. The mobo will do a X config at x8 on both ports (x16 on one obviously).
I don't want to loose performance though I have read that 1 GTX 480 will almost or fully saturate a 2.0 port at x8 - if this is true, a 6850 shouldn't.
Does anyone have any definitiveness towards that or information about a x8 saturation? I can't seem to find anything besides word of mouth.
-b

 

[jefe323]

you'll probably see around a 5% performance drop

 

[deweycd]

You should have no problems with running two 6850 at x8. There is minimum difference between x16 and x8 as no card really does saturate x8.

 

[blacken666]

Beautiful.
The 6850's are attractive because of the required 1 6-pin power connector. That should keep the case nice and tidy and help the 1900x12 resolution out a bit. I oddly enough have never tried to do a SLi/XFire config until now - I've always had one mid-high range GPU. I've been gaming since my 1mb S3 onboard so this is going to be interesting.
Has the micro stuttering issue been resolved in the last few years?

 

[17seconds]

This article describes your scenario:
http://www.hardocp.com/article/2010/08/23/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x8x8/

"It seems that at 2560x1600, even with 4X AA, there was absolutely no difference between x16/x16 and x8/x8. This is good news if you game at x8/x8 on a single display configuration at 2560x1600 and below. You simply are not missing anything, and moving up to x16/x8 or x16/x16 will yield no performance improvements or gameplay differences, even on the fastest GTX 480 SLI."

"The Bottom Line
If you are running on a 30" display at 2560x1600 or below, an x8/x8 SLI or CFX configuration will perform the same as a x16/x8 or x16/x16 configuration."

 

[Andon48]

I have a GTX 460 in the X8 slot on my motherboard because there is some interference with the ram slots when it's in the top slot. I've done a few benches both ways and the difference between X16 and X8 is about 1%. I'd say you will lose maybe 2 or 3% (if anything) with X8/X8. Not enough to worry about at any rate.

 

[blacken666]

This article describes your scenario:
http://www.hardocp.com/article/2010/08/23/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x8x8/

"It seems that at 2560x1600, even with 4X AA, there was absolutely no difference between x16/x16 and x8/x8. This is good news if you game at x8/x8 on a single display configuration at 2560x1600 and below. You simply are not missing anything, and moving up to x16/x8 or x16/x16 will yield no performance improvements or gameplay differences, even on the fastest GTX 480 SLI."

"The Bottom Line
If you are running on a 30" display at 2560x1600 or below, an x8/x8 SLI or CFX configuration will perform the same as a x16/x8 or x16/x16 configuration."

Thanks for that. I'm almost thinking about doing a crossfired 6870 because of it.