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Questions about crossfiring 5870s

Last response: in Graphics & Displays
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February 24, 2011 4:02:37 PM

Hello all,

First off, my specs:

Gigabyte EP45-UD3P
Intel C2Q Q9550 @ 3.4GHz
HIS Radeon HD 5870 1GB
8GB Mushkin DDR2 800
PC Power & Cooling 750W PSU


When I first built my system, I had a single 4870 512mb. Then after a while I upgraded to a second 4870 and noticed a huge performance increase. After the 5870 came out, I bought one and it ran a bit faster than the Crossfired 4870s. Now I just bought a second videocard off newegg (Shellshocker deal).

This card:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Sapphire HD 5870 Eyefinity 6 edition 2GB.

My first question. Will these two cards be compatible in crossfire? From what I know, if it is from the same product line (5800 series), then it should crossfire. I do know that the 2GB card will scale its memory down to 1GB, but for less than $200 I really couldn't pass this deal up.

Second question. I remember the 4870s being huge power-hungry beasts. Something the 5870 seemed to improve on. Will my PSU have the power to run both of these cards?

And third question. My motherboard only has one true x16 2.0 slot, when in crossfire, both cards will run at x8 x8. Will this bottleneck the cards at all? I have seen several benchmarks/threads saying not much at all, as little as 5%. What kind of performance increase can I expect with the addition of this card?

Thanks for your input.

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February 24, 2011 4:10:44 PM

Yes they'll be compatible. And yeah, you'll lose that extra VRAM unfortunately.

750W is sufficient but that brand isn't top notch. That said, according to this review it has 60A on the 12V which is pretty decent. I wouldn't recommend overclocking everything to the max or adding a 3rd card but you should be fine even with a bit of OCing if you choose.

8x/8x is fine. The review here on Tom's showed they get bottlenecked by around 5% like you said. But they'll still be fast. With my 5850s I saw around 60-80% FPS increase depending on the game. In synthetics (like Furmark) it was ~90% higher FPS.
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February 24, 2011 4:13:23 PM

No you must crossfire 2 cards of the same memory size.if you did i think that only 1gb on per card would be recognized not 2gb and 1gb.
for second question i would say that yes it would be great if you would crossfire the two 5870s.it would be much faster than hd 5970 and quite better than any other setup of xfire.

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February 24, 2011 4:24:05 PM

wolfram23 said:
Yes they'll be compatible. And yeah, you'll lose that extra VRAM unfortunately.

750W is sufficient but that brand isn't top notch. That said, according to this review it has 60A on the 12V which is pretty decent. I wouldn't recommend overclocking everything to the max or adding a 3rd card but you should be fine even with a bit of OCing if you choose.

8x/8x is fine. The review here on Tom's showed they get bottlenecked by around 5% like you said. But they'll still be fast. With my 5850s I saw around 60-80% FPS increase depending on the game. In synthetics (like Furmark) it was ~90% higher FPS.


Actually PC Power & Cooling seems to be a very reliable brand for me. I've used it in most of my builds I do for other people (If I don't use them, it's usually Corsair), and so far I haven't had a problem at all. Very quiet, well built PSUs IMO.
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February 24, 2011 4:48:32 PM

definitely right.well if you have both gpus right now,try it and tell us what happens then!
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February 24, 2011 5:59:20 PM

Haha I wish I had both right now. I just ordered it earlier today after doing some research. I will post results after though.

Hell, with these two cards I might be able to run Crysis 2 on medium!

My bottleneck now is most likely going to be my RAM/CPU/MOBO. Hopefully Intel fixes sandy bridge quick =D
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February 24, 2011 6:02:36 PM

^ I would be flabbergasted if you couldn't run it at max.
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February 24, 2011 6:03:55 PM

just take your cpu above 3.8ghz or upto 4.0ghz,then there would be no bottleneck.you would be able to max out crysis 2 now,i am fully sure.
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February 24, 2011 6:24:25 PM

wolfram23 said:
^ I would be flabbergasted if you couldn't run it at max.



Hahah yeah I know, it was more of a joke I guess. Since Crysis took such a beast of a computer to run back in the day people act as if Crysis 2 is going to do the same.
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February 24, 2011 6:26:41 PM

well no not this time.crysis 2 is nvidia sponsored so i am sure that ati would be screwed by this game with less fps.
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March 6, 2011 3:38:52 AM

Best answer selected by Pigbearman.
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March 9, 2011 9:31:58 PM

I have a 750w Corsair psu and I also have the 2gb Sapphire 5870 that I am going to crossfire soon. So if your psu is powering your system well, then please! Do tell!
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March 10, 2011 12:26:58 AM

Yep, having absolutely no problems with the setup so far. If only AMD had better drivers though.
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