Dual core or quad core ?

Hello.
I'm going to buy a second hand pc for my son.
I'm thinking of these two ;

Duo core E6850 3ghz, 2G Ram, 2x asus 7900GTX. 150 euro.
Amd Phenom II x4 940S AM2+, 2G Ram, no GPU. 150 euro.

I have a hd 6870 laying around and can put that in the Phenom.

I would like the 2x Asus but i know the Quad core is better.

Which one should i buy and what's the performance difference between phenom II with 6870 and intel dual core with sli 7900gtx ?

Thanks in advance.
 
Solution
The 7900GTX is a very old card and is 10 tiers below the HD 6870 on Tom's graphics card hierarchy. Without a doubt, the Phenom system with your 6870 would perform far better than the other system. If you add in your video card and maybe upgrade it to 4 GB of ram later, the Phenom machine will be a very good gaming box.

Edit: Just realized it had 2x 7900 GTX. l still think the 6870 would run faster though (and it would be much more energy-efficient).
The 7900GTX is a very old card and is 10 tiers below the HD 6870 on Tom's graphics card hierarchy. Without a doubt, the Phenom system with your 6870 would perform far better than the other system. If you add in your video card and maybe upgrade it to 4 GB of ram later, the Phenom machine will be a very good gaming box.

Edit: Just realized it had 2x 7900 GTX. l still think the 6870 would run faster though (and it would be much more energy-efficient).
 
Solution
Oke, thought so to, but the sli thingie got my interest since i never had that before.

@384 bit ; I'm more than confident my son will be over the moon indeed, he had a P3, 667 Mhz before . . . 😀 What does the AM2+ means btw ?
And i don't have to buy a new card, so i won't buy the 7900 alone, it's comming with the pc. ( the dual core ) I have got the 6870 allready.

Would the amd setup be faster because of the 6870 or because of the quad core, because i think i have heard sometime that gaming don't use more than two cores or something, can be wrong tho.
 
AM2+ is just a socket from AMD.

The main differences between Socket AM2 and AM2+ socket processors are as follows:

HyperTransport 3.0 operating at up to 2.6 GHz
Split power planes: one for the CPU cores, and the other for the Integrated Memory controller (IMC). This will improve power savings, especially with integrated graphics, if the CPU cores are in sleep mode but the IMC is still active.

Basically the difference between AM3 and AM2+ is that lack of DDR3 controllers on the AM2+.
 



Yes, that was definitely true for a while, but more and more games are now supporting triple and quad core. There was an article a while back on this site that showed 3 cores is the least you should have for a gaming PC. Any less than that, and you will get reduced performance even if you have a top of the line video card.