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

[randomkid]

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

 

[AdrianPerry]

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.

 

[4eyed]

From what i read there's almost no difference between x16 x16 and x8 x8. i5 all the way!

 

[bullgarian]

get the intel you will not regret it

 

[thently]

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

 

[DoomsWord89]

Indeed, you would benefit more from the performance and OC capabilities of an i5 than you would from operating at 16X16.

 

[de5_Roy]

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.

 

[randomkid]

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.