Dual 7850s on x16 and x4 [ASUS P8Z68-V LE]

I have a system with a single 7850, and am possibly going to buy another to run CrossFire. The problem, however, is that the second PCIe slot (Supposedly also x16) appears to have a "x4 mode". I'm wondering if there will still be a significant increase in performance if ever I run CrossFire with a second 7850, and how badly will it compare to running CrossFire on two x16 PCIe slots?

For your reference:
MOBO - http://www.asus.com/Motherboard/P8Z68V_LE/#specifications
GPU - http://www.asus.com/Graphics_Cards/HD7850DC22GD5/

Thanks in advance to all those who will reply.
3 answers Last reply
More about dual 7850s asus p8z68
  1. You will still get an increase in performance if you crossfire with another 780 but noy as much as running both cards on two x16 pcie slots. The performance difference will probably be 10-15%.(my guess)
  2. I believe the x4 bandwidth isn't meant for GPUs(or at least mid-high end cards), so it's going to bottleneck the 2nd GPU giving you at most 5-10% increase in performance.
  3. I know it's said that anything under 8x will be bottlenecked for a GPU, but when I did my two 4870s 16x/4x I still saw a worthy improvement (50-60% roughly). I have an ASUS M4A78 Plus. I would still recommend 8x or 16x in both slots, but it can be a cheap upgrade now, then you can get a new mobo later.
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