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How bottlenecked would a PCIe 3.0 x16 card be in a 2.0 8x slot?

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November 1, 2013 1:03:01 PM

My motherboard has one only PCI Express 2.0 x16 slot and two PCI Express 2.0 x8 slots.

I would like to SLI two GTX 760's, but how bottlenecked is a PCIe 3.0 x16 card going to be living in a 2.0 x8 slot? Would I get better performance from a single GTX 780 instead of SLIing the 760's in this case?

Processor is a i7-980 Gulftown 3.33GHz Six-core, so I should be fine there.
a c 195 V Motherboard
a c 87 Î Nvidia
a c 255 U Graphics card
November 1, 2013 1:09:20 PM

You will see no bottlenecking at all with 2 x GTX 760s in your PCI-E 2.0 x8 slots. Now I have not read up on GPU scaling on PCI-E generations since the GTX 680 was the flagship card so with an R9 290X, GTX 780 or Titan there might be a slight bottleneck but as of my last reading on the subject the PCI-E standard was well ahead of what is necessary for even high end graphics cards.
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a c 137 V Motherboard
a b Î Nvidia
a c 147 U Graphics card
November 1, 2013 1:30:50 PM

I'd have to look up the data, but I don't think you'd be bottlenecked in that scenario, or if you were it would be quite small. I know a single HD7970 or GTX680 didn't max out a PCIe v2.0 x16 slot. My gut tells me there's be a SMALL amount of bottlenecking in some scenarios such as 5%.

However, while SLI has improved it's still not as smooth as a single card. My advice is THIS card:

EVGA GTX780 3GB (the 967MHz Base Clock model). It's $500.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

BENCHMARKS:
http://www.guru3d.com/articles_pages/evga_geforce_gtx_7...

*No 760 SLI in this list. You can estimate though by averaging say 70% improvement. Performance by this estimate is thus the SAME except you have:
- less RAM for 760 SLI
- more NOISE for 760 SLI
- way less performance when SLI doesn't work, or when the driver support isn't optimized
- microstutter (not the problem it was but a single GPU is smoother)
- about the SAME price for 2x760 SLI as a single EVGA 780.

Summary:
I can find no good reason to get 760's in SLI now that this awesome EVGA 780 card is $500 and is better in every way.

*Battlefield 4 will use more than 2GB when you crank up the quality. SLI clones data between cards so 2x2GB is still 2GB usable.
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a c 195 V Motherboard
a c 87 Î Nvidia
a c 255 U Graphics card
November 1, 2013 1:38:39 PM

^ I agree unless you already own the 760s. Also the GTX 780 is getting a refresh as the 780 Ghz Edition and those should be available in a week or 2. A new stepping means higher clock speed.
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