Asus P8P67-M Pro & crossfire

[nBkDax]

hey guys i just recently bought a crossfire setup (2 6950's) and was reading that the lane speeds of the Pci interfaces differ i loaded up GPUz and saw that the first card is running at 16x and the second card is running at 4x, now i heard that 8x by 8x performs better than 16x & 4x.
so i want to try this out and run both cards at 8x to see if there actually is any difference in performance.........
but i have no idea how to get both cards to run at 8x and was wondering if i maybe put the one card in the wrong slot as there are 3 on the motherboard.
so here are some pics of my setup



now the only thing that is worrying me is moving my bottom card up to the white slot, the cards will be right on-top of each other with the bottom card blocking the tops airflow??

also i was wondering if its not better to just leave the cards at 16x, and 4x for games that don't support crossfire logic being that the main card will have better performance for these games as its sitting at 16x? this make sense? or do you guys think i am just nitpicking and the performance gain will be negligible?

 

[nBkDax]

sigh it seems the manual says i am using the wrong slots (should use the top 2), i am still hesitant to do this tho due heat, cooling and how much air the top card will get ???

anyone else running 2 of these in crossfire right on top of each other ??

 

[(FIH) The Don]

you wont kill the cards, and you should be able to run them side by side

they will get hotter, but they wont die, dont worry

 

[nBkDax]

but what i am saying is is it worth the performance gain?
how much diff is there between a 16x 4x setup vs 8x 8x??

 

[cadaveca]

but what i am saying is is it worth the performance gain?
how much diff is there between a 16x 4x setup vs 8x 8x??

Depending on the app, you'll only get 50% of the second card's performance in 16x4 versus an 8x8 setup. that means if in 8x8 you get 100FPS, in 16x4, sometimes, you'll only get 75FPS.


If these boards stop showing up at my door soon, I'll be looking to do that exact compare with the majority of recent titles. I've got P67 16x4/8x8, and 9-series AMD @ 8x8 and 16x4 to do it with, so I can show both AMD and Intel numbers.



But, work before pleasure.

Also, get a fan on the end oppposite the outputs blowing along the length of the cards to help keep the cards cool, if you put them in the slots next to one another.

 

[nBkDax]

nice moved it up a slot put in an extra fan and bam! running 8x 8x
Must say i am impressed also never thought to see such a big difference

Before
3Dmark vantage score of H23143 (image uploaded stopped working :/)

After