Will pci-e 2.0 @2 times x16 lane cf/sli be faster than x8 mode 2.0

[jamespcguy]

Can any single gpu's today (such as the hd 5870) not including sli on a card solutions, saturate the bandwidth of pci e 2.0 x16 lane or x8 lanes. I want to know if i need to get a mobo with 2 x16 lanes of pcie 2.0 lanes, or if x8 lanes of 2.0 will be sufficient for today's standards of gpu's if i were to run hd 5850's (or something similar) in crossfire. So basically will any graphics cards around be able to bottleneck the bandwidth provided at x8 lanes of pcie 2.0, and if not when would it start to bottleneck x4 lanes of 2.0? or..

 

[smithereen]

I think you should be fine with 5850s, wouldn't go higher than that though.

 

[Maziar]

The difference between dual 8x and dual 16x isn't much in most games,here is a review:
http://www.tomshardware.com/reviews/core-i5-lynnfield,2379-5.html

however 4x slot isn't good,some motherboards support crossfire @ 16x4x which won't perform well compared to dual 8x/16x and will give a performance hit
http://www.tomshardware.com/reviews/crossfire-pci-express,2095.html

 

[JeanLuc]

I think you should be fine with 5850s, wouldn't go higher than that though.

Please don't say that as you obviously haven' t bothered to do any sort of research.

The truth is there is no difference between x8 and x16 (unless you call 1 FPS or less a performance hit, barely worth mentioning IMO) just look at these Crysis benchmarks and that's with a HD5870 the most powerful single GPU card on the market. It turns out you have to go all the way down to x4 to see a measurable performance drop and even then it's not that dramatic.

 

[jonnyberthiaume]

Just take a look at this article: http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/

It does show you everything you need to know about performance scalling over X1/X4/X8/X16 setup. In summary, X8 is about 2% slower than X16 and X4 is about 5%.

So do the maths,

5% slower on 100 FPS = 95 FPS = No difference, crazy fast

5% slower on 50 FPS = 47 FPS = No difference, still as fast

5% slower on 25 FPS = 24 FPS = No difference, still unplayable

...

So if you scale this over crossfire, you can conclude there is no noticeable difference whatsoever between X4/X8/X16 setups.

 

[smithereen]

5% is significant. Significant enough to be charged a premium. Most companies release a 'house' brand of graphics cards pre-OC'd 5-15%. The difference between the Phenom II 955 and 965 is 7%.

 

[jonnyberthiaume]

5% is significant. Significant enough to be charged a premium. Most companies release a 'house' brand of graphics cards pre-OC'd 5-15%. The difference between the Phenom II 955 and 965 is 7%.

Well, let me disagree. Sure, 5% is better than nothing and if the price is right then I would invest in the better solution. But, and this is a big big but (no jokes intended), 5% won't be enought to actually see a real world difference. Even more, 5% is for a PCI-E X4 not X8, X8 is only at most 2%. Take it anyway you want, paying a good board X8/X8 175$ over an X16/X16 board 275$ (P55 vs X58) is a really great opportunity. No way in hell 2% is gonna pay itself for an premium of 100$(57%)!

And for the record, I know most companies releases pre-OC'd 5-15% video card, but it's more a marketing stuff. Don't get me wrong here, if I have the choice between 2 models at the relatively same price, I'll get the faster one, but then again I wouldn't buy a 2% faster product for a 50$ premium. 2 freakin percent! Think about it 2 seconds, that makes no sense at all! How can you see the difference between 100 FPS and 102 FPS?!? You can't! That's impossible for any human, as freaky he is...

Those oc'd models are marketed for hardcore enthusiast for whom money isn't a factor. For 99% of the rest of the world, it makes no sense.

For those enthusiast out there, if money isn't a factor, then go get it, I envy you, you'll get the faster product. Really really nice for you. But I can't afford to pay a price premium of over 50% for less than 10% perfomance. That's a fact, that's undeniable. Accept it. I just wanted to give my opinion about the X8 performance to jamespcguy.

Now for jamespcguy, a more complete answer to you would be: it depends on what are your needs. If your an hardcore enthusiast, then get the X16 without a doubt. You can't decide on which setup you want only on the PCI-E setup anymore. I, personnaly, will choose a X8/X8 setup P55 (Intel) setup for my next build. Why? Because I know PCI-E 3.0 and USB 3.0 will hit market maybe next year. I won't wait that much before buying my system. So I will take the "cheaper" route with an I7 860 with in mind of changing my CPU/RAM/MOTHERBOARD in 2 or 3 years, when those technology are going to be mature. Right now, a single ATI 5870 will play all my games and next year ones at full setting over 1920x1080. With a single card, the board will run it at X16 so that won't make a big difference whether I use a X8 or a X16 setup. But, I like the cheaper price, the low power consuption and the low impact (2%) performance if I decide to go with 2 cards. Some will say than an I7 920 would be more futureproof, I'd reply not necessarily. In 2 or 3 years, I'll want the new tech around and I won't spend 600$ to 1000$ on a Gulftown, so my current build satisfy my needs. The day the new Gulftown will be down to 300$, if it happens, there will be another new socket or a new CPU from Intel that will destroy the old one anyway.

What I'm trying to say is you have to determine what want to do with the board. If you have a budget, either X16 or X8 setup will do, as long as they fit in your budget. If you don't have a budget and money isn't a factor, then go for the X16. That's yours to decide.