If i had 2x 5770 how muc performance adding a third

No you will not get the same boost by adding a third, more like 20%, and say you had 3 cards and added a forth wouldnt do much at all. scaling seems to get worse with the more cards you add.

If you had 2 x 5770's and had the money for a third then I'd sell the 2 x 5770's and with the money from the sells and the money for the third card you could buy a monster single card.

I wouldn't start off with a crossfire configuration. Get an HD5850/70 instead of 2 HD5770s(unless you already have one.)

well thing is in 2 years time id upgraded to dx12 if its out so geting another card down the rd is unlikely for a crossfire cinfig with a 5850. but id get more performance now with 2x 5770's. but your saying if i ever needed to add a third card it would be somewhat useless to add a third card if i ever got to that piont?


also wich would be easyer to ebay down the rd, a 5850 or 2x 5770's

Just simple logic will let you know it wouldn't have the same boost. When you add a 2nd GPU, you are doubling the GPU's you have, but adding a 3rd is at best adding 50% more power. Of course there is a loss of performance with each processor, so it's less again.

Also keep in mind, many boards lose bandwidth when you use more of the PCIe 2.0 x16 slots.

Anyways, it's definately less of a boost than adding the 2nd, and 20% may be about right, it could even hurt your performance adding the 3rd depending on your motherboard.

I agree with jyjjy, a single 5850/70 is a smarter choice, it'll use less power, produce less heat and you wont have any scalability problems, as some games dnt take advantage of multiple cards.

An HD5850 OCs very well. Close to the performance of an HD5870(or higher if you up the voltage.) It will also use less power and will have no crossfire scaling/compatibility issue.
The power of two HD5770s in crossfire is overstated a bit because of it's limited memory bandwidth which can make it struggle at times to keep up with the processing power the 2 GPUs provide. This means that while the average frame rate is high the minimum frame rate suffers which is important for smooth game play. Here's a good article to check out;
http://www.xbitlabs.com/articles/video/display/radeon-h...

I am running two 4870`s in crossfire,now i know its not the card that you mention but its more the Crossfire issue,the shop i went to i asked the question on how much i would gain from a second card and he said i would be lucky to get 30%,realistically it would be more like 20% from the second card.

It all depends on what game you play, For instance when i had 2 x4870's i noticed a huge gain in CoD4 somehow more than 100% went from 91FPS to 200+ FPS, But in other games there was no benifit at all.

Adding a third card is rarely a good idea, at least not for the money it costs. For that matter, crossfiring usually isn't a good investment unless you're just adding a second one to an older card that you already have (e.g. you have a 4770 or 4850 and adding a second one will get you to the 4890 or 5xxx series' performance range).

Basically, for just about any card that you can buy two of and crossfire, there's a single card out there that performs just as well and costs the same or less.

Also, with most motherboards I've heard of, at most the first two cards will operate at x16; add any more and some or all of the slots will be downgraded to x8, x4, or x1 depending. A lot go x16/x8/x8, a lot go x16/x16/x1. So you'll lose some performance there too, in addition to the other issues people have mentioned.

http://www.guru3d.com/article/radeon-hd-5770-in-3way-cr...