PII X4 3.4GHz +x16x16 CF vs i5 2500K +x8x8 CF

My current build is an MSI 790FX GD70 running an unlocked & OC'd PII X3 720 (quadcore@3.4Ghz) with 2x6950 2GB mainly used for gaming on a 5760x1080 tri-monitor set-up. This motherboard supports x16x16 Crossfire.
I have a new i5-2500K on an MSI Z68A-GD55 which can only support x8x8 Crossfire.

Will there be more benefit if I move the 2x6950 2GB cards to the Z68A-GD55 to give a CPU boost even if the PCIe slots can only run x8x8 ( note that I am running in eyefinity ).
Or should I keep the current set-up relying on my PII X3 720 (quadcore@3.4Ghz) to drive the 2x6950 but on x16x16.

I do not consider buying any more part & will make do with what I already have. Whatever system do not have the 2x6950 will be used for browsing & an HTPC.

Thanks!

Randomkid
7 answers Last reply
More about 4ghz x16x16 2500k x8x8
  1. The i5-2500k (especially when OC'd 4.5GHz+) should show much more improvement over the Phenom II x3 even with the more limited PCI lanes running x8 x8.
  2. From what i read there's almost no difference between x16 x16 and x8 x8. i5 all the way!
  3. get the intel you will not regret it
  4. Yes the intel setup for now is the way to go 8x8 will not hurt you at all. It only becomes apparent in a big way on dual cards.

    Thent
  5. Indeed, you would benefit more from the performance and OC capabilities of an i5 than you would from operating at 16X16.
  6. if you can wait till ivb get out....
    you could get ivb core i5 -k cpu and a motherboard with intel z77 chipset - which will let you use pcie 3.0 x8+x8 (similar to pcie 2.0 x16+x16, speedwise).
    the core i5 2500k bottlenecks cfx cards less than phenoms (and fx) do, may be ivb will bottleneck even less.
  7. There is this useful link: http://forums.overclockers.com.au/showthread.php?t=930170
    which states
    "Now there doesnt seem to be a great deal of saturation on those x8/x8 PCI-E slots going on there. If my math is correct the overall avearge FPS difference between x8/x8 and x16/x16 in these benchamarks is:
    -Just over 2% @ 1920 x 1200
    -Just under 6% @ 6036 x 1200"
    This is for 2 x HD 5870. Recognizing that 2 x HD 6950 CF is more powerful than 2 x 5870 CF, then I guess the performance hit will be more in terms of fps.But on the other hand, my resolution is smaller at ~5760x1080 so overall fps will still be higher than that in the review.

    Another review: http://www.hardocp.com/article/2010/08/23/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x8x8/3
    states
    "The only time that you should even be slightly concerned about running at x8/x8 is when you move up to a multiple display setup. When we pushed the GTX 480 SLI at 5760x1200 we saw up to a 7% difference in performance between x8/x8 and x16/x16, in favor of x16/x16, but that was in one game only."
    This is for 2 x GTX 480 but pretty much say the same (at least for AVP).

    But in any case, the vote is unanimous so off to i5 2500K I go. :)
    Unfortunately my board is not G3 so I'm stuck to PCIe G2 x8 x8 even when ivb arrrive...

    Thanks everyone for the input & comments.
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