Pci-e x4 question

would a higher end video card like an x1800xt be bottlenecked by a pci-e x4 slot compared to a x16 slot? this is in reference to a few motherboards that come with a x16 size slot meant for video cards but only have x4 tied to it
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  1. There wouldn't be a noticable difference.

    The older AGP interface still doesn't even limit videocards.
  2. I would think that high-end gpus would benefit from 8x over 4x especially in xfire/sli setups. The gpus may not saturate an 8x, but from what Ive read they do saturate 4x.
  3. Some numbers:

    AGP 1x has 266MB/s bandwidth (32bit @66MHz)
    PCI-e 1x has 250MB/s (2.5Gbps, 10bit average to trasmit a byte)

    So AGP 8x runs @2.1GB/s, PCI-e 4x @1GB/s

    At the current time there is no graphics card that can saturate an AGP 8x: the fastests use at most 70%, that is 1.5GB/s.
    But PCI-e 4x runs in full-duplex: it can transmit and receive data @1GB/s in both directions, while AGP is half-duplex, so they are virtually equivalent.

    Anyway, an 8x slot is required for a master SLI card.
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