x8/x8 vs x16/x16

[zeliscar]

Hey, I'm building a new comp and because I'm kinda of a beginner I'm having trouble picking my motherboard. (specs: i5-2500K, 2x Radeon HD 6970)

The two boards I'm comparing are Gigabyte's GA-P67A-UD4 and UD7.
My question is:
Is the difference between x8/x8 and x16/x16 PCIe worth paying almost twice as much?
What about 3-way Crossfire in UD7? If I already have two cards now would it be worth buying it so that I can add third in the future?

 

[SirGCal]

I did some testing with this myself a while back and only saw up to a 6% difference at extreme stress levels (res and toys). Now that test wasn't with 6xxx series cards but. Still I doubt it would be much. The PCIe link isn't the limiting factor in Crossfire. And the 6x series is so much better in crossfire, I doubt you'd see any real difference at all without measuring it specifically. But this is just speculation for this specific scenario. So you have to decide if the cost is worth it for yourself. If you find other more accurate benchmark tests with these items; that would be interesting but I highly doubt you'd see any significant difference between them.

 

[Spikesoldier]

My question is:
Is the difference between x8/x8 and x16/x16 PCIe worth paying almost twice as much?
What about 3-way Crossfire in UD7? If I already have two cards now would it be worth buying it so that I can add third in the future?

not worth it at double price. i think that a 580 shouldnt take much a hit at all @ pci-e 2.0 8x/8x SLI mode. with improved scaling on both SLI and CF on the newest generations, the third card becomes more appealing.

intel's p55 and p67 platforms can ideally only handle two cards at 8x speed or better, unless like with the UD7 there is a NF200 chip that allows for more PCI-e lanes. three cards would be better accommodated natively by the X58 platform's successor.

if the difference is twice the price id pocket the savings and invest it towards new cards when you need more gpu power, although it may be worth it to you if you want to pay the premium for a third card and the more expensive board right now.

 

[Skott]

I remember back when x16/x16 mobos came out and there was a lot of talk about how good it was compared to x8/x8. Back then testing proved that you had to get 1920x1200 res or higher to see the extra benefits and even then the extra performance was not huge. Its my understanding that hasnt changed much.

Now as far as whether to go single GPU or dual GPU depends on a couple things. 1)Resolution. 2)Single monitor or Multi-Monitor (Eyefinity/3D Surround). If you're going more than 1900 res or multi monitor (which is also high res) then SLI or CF becomes more attractive.

I would say if you are going with 1920x1200 or less you are better off with a single good card. Whether the mobo is x8/x8 or x16/x16 doesnt matter.

As far as triple cards or quad cards, I'm not too knowledgeable but from what I hear the scaling up performance vs price is not all that attractive or cost effective. Stick with one or two GPUs is my advice.

 

[MagnusTheBrewer]

The folks over at [H] did a series of articles on this very thing. You can find it here.
I don't think you'll lose any performance going with the x8/x8 board.