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1155 Mobo for Crossfire X?

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July 14, 2011 5:20:02 PM

Hey all, about to buy a new i5 2500K and a HAF-922 case, and I wanted some help choosing a motherboard, I want to keep it around the $150-180 price point. I was looking at a good MSI board but the problem was one of the PCI-E slots was x16 and the other was x8. Now excuse me if I'm wrong as I'm not entirely sure, but 2 x16 slots will get you higher performance than 1 x16 and 1 x8, correct? So i'd be looking at a board with 2 x16 slots on it, if my knowledge is correct.

If it helps I plan to be using 2 XFX 6870's for my configuration. And the board would preferably be ATX (Duh :p )

Cheers!

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a c 715 V Motherboard
July 14, 2011 7:03:11 PM
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The current Sandy Bridge has only 16 PCIe lanes native to ALL LGA 1155 - period, now there are some LGA 1155's with the added NF200 chipset to 'create' additional PCIe lanes - problem it adds some measure of latency.

The upcoming LGA 2011 and SB-E CPU offers 32-lanes, Quad-Channel, and also the PCIe 3.0 which is effectively Double-Bandwidth to the current PCIe 2.0 -- in other words the equivalent bandwidth to 64-lanes of PCIe 2.x.

Q1 2012 the Ivy Bridge adds PCIe 3.0 but is still limited to 16-lanes to the GPU.

The HD 6870 is a good mid-level GPU, but there's no way it will saturate 16 lanes and not even 8-lanes. That said, look for your favorite x8/x8 P67 or Z68 MOBO; Gaming IMO stick with the P67.

Here's 4 good MOBO's -> http://www.newegg.ca/Product/Productcompare.aspx?Submit...|13-157-229^13-157-229-TS%2C13-130-574^13-130-574-TS%2C13-131-771^13-131-771-TS%2C13-128-478^13-128-478-TS

My pick in your stated price range is the MSI P67A-GD65 (B3) -> http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...
a b V Motherboard
July 14, 2011 8:27:02 PM

The performance difference between cards on 16X,16X lanes vs the same cards on 8X,8X lanes is roughly 5% which in real world would translate to a 2~3 fps difference. As you can see, not a big deal. No point spending extra for a 16X+16X motherboard.
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a b V Motherboard
July 14, 2011 8:38:15 PM

Yes it's best to have 16x/16x, but in the case of Sandy Bridge the increased latency added by an NF200 chip pretty much offsets any gains in bandwidth from having 16x/16x making it not worth the extra cost unless you want to do 3 or 4 way SLI, which you do not.
July 14, 2011 11:40:37 PM

Thanks all, one last question, do you know if an XFX 650w power supply will be sufficient for an i5, 2 HDD's, 6gb Ram, a DVD drive and 2 6870's? That's what I've got right now and I'm trying to spend as little as possible by keeping what I can.

Thanks!
a c 715 V Motherboard
July 15, 2011 12:33:51 AM

PSU Sizer -> http://www.corsair.com/learn_n_explore/?psu=yes

A 750W would be the minimum PSU that I would choose, and if you're going to OC both the CPU and GPU's then 850W to 950W. I recommend a PSU to run between 50%-60% which is the most efficient and adds to longer life.
a b V Motherboard
July 15, 2011 4:24:42 PM

-_- well it should be o.k but I think it's more of a question if you have enough connectors :D . After all two 6870s use about 100W less than my two 5870s. Also keep in mind these measurements are taken from the wall (there is some loss in the PSU as it's converted ie 80% efficiency means 20% loss) so the power used inside the system is a little less.

http://www.guru3d.com/article/radeon-hd-6850-6870-cross...

So yes even if you overclock your CPU you would really only be using between 60-70% of your PSUs capacity worst case. If you overclock your GPUs it will be a little more.
a c 715 V Motherboard
July 15, 2011 4:44:03 PM

I really hate PSU discussions. You can run a Camry on a track @ 120 MPH and you can run a Porsche 911 @ 120 MPH - try them both for several hours.


July 16, 2011 5:10:15 AM

I would recommend a 750W minimum for your build. I am running an i5 2500 and R6870 CrossFireX (neither overclocked... yet) on a Corsair TX-750 and it seems stable. I would not go for anything lower than that.

This RaidMax power supply looks pretty good. It claims to be 80+ Gold certified at 850W with 4 x 4+2 pin connectors. 6870 Crossfire will take 4 x 6 pin connectors so you are fine there.
http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...
July 17, 2011 2:06:53 AM

Thanks for all your help everyone, I've gone ahead and ordered everything! Will get better PSU and second 6870 in the future!

Mobo- MSI P67A-GD65 (B3)
July 17, 2011 2:07:34 AM

Best answer selected by Battery9000.
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