So I added a second GTX 680 4GB in SLI. Here's how it works with modern games.

[Smart_Guy]

Yeah, I got it for $101.33 USD total cost.

I did some benchmarks and the details are below.

Relative system specs.:
CPU: Intel Core i5 3570K 3.4GHz overclocked to 4.2GHz for these tests
RAM: 16GB 1600MHz
Mamaboard: ASRock Extreme6 Z77
PSU: Cooler Master Silent Pro Gold 1000w
Video card 1: MSI GTX 680 Twin Frozr 4GB O[FONT=&quot]C (the original)
Video card 2: [/FONT]EVGA GTX 680 Classified 4GB S[FONT=&quot]C (the added one)

Games crash sometimes so I reduced GPU clock to matching 1058MHz with boost to see how it works.

Used software:
[/FONT]

1- Unigine Heaven[FONT=&quot].
[/FONT]​

2- Grand Theft Auto 5[FONT=&quot].[/FONT]​

3- The Witcher 3[FONT=&quot].[/FONT]​

4- Doom[FONT=&quot].[/FONT]​

5- Gears of War 4[FONT=&quot].[/FONT]​

Unigine Heaven (DX11):

1080p (max settings)
Min. 26
Avg. 71
Max. 155

1440p (high with tessellation normal)
Min. 22
Avg. 49
Max. 108

4K (medium with tessellation moderate)
Min. 7
Avg. 25
Max. 54


Grand Theft Auto 5 (DX11):

1080p (max with MSAA @4X)
Min. 44
Avg. 55
Max. 73

1440p (max with MSAA @2X)
Min. 44
Avg. 52
Max. 60

4K (high settings with high res shadows off and people variation min.)
Min. 33
Avg. 38
Max. 46


The Witcher 3 (DX11):

1080p (ultra with no hair works)
Min. 48
Avg. 61
Max. 91

1440p (ultra, no hair works and foliage range high)
Min. 39
Avg. 48
Max. 75

4K (high, no hair work and foliage range high)
Min. 21
Avg. 26
Max. 44


Doom (OpenGL):

1080p (ultra)
Min. 64
Avg. 81
Max. 111

1040p (ultra)
Min. 41
Avg. 50
Max. 74

4K (ultra)
Min. 18
Avg. 24
Max. 38


Gears of War 4 (DX12):

1080p (ultra)
Min. 49 (44 on one card)
Avg. 83 (55 on one card)
Max. 110 (65 on one card)

1440p (ultra, both world and character texture details on high)
Min. 41 (30 on one card)
Avg. 55 (35 on one card)
Max. 64 (43 on one card)

4K (medium)
Min. 29 (20 on one card)
Avg. 39 (25 on one card)
Max. 44 (30 on one card)


Conclusion:
I did some research on GTX 1060 6GB and found my results are similar. Maybe no all games support SLI, but all games I'm playing now do. Probably all future games will too given some time. I don't really buy games once they are released anyway. With some tweaks here and there, 4K could be playable too. But generally it is a 1080p setup if high quality settings are desired. I think my build can now live 3-4 years more per my preferences in games.

 

[Cortb]

Does your board have enough pcie slots to do a 3 or 4 way SLI? Probably no need right now, but in another couple of years when the prices come down further on the gpus it might eeke out another couple of years of usefullness...

 

[Smart_Guy]

There is a third slot, but with these big cards two is all I can fit. But even if it fits, it wouldn't be good. The CPU can't handle a third one (I'm already getting a bottleneck in one area in Dark Souls 3), the mobo's chip set is a Z77 with limitations that three cards will have the third work at PCI-E X4 only which will hurt the performance of a GTX 680 so it won't be cost effective, and actually the gain will be little if not worse due to the above and lack of support as per the reports. A second card add ~80% performance at least in all games I tried. A third adds no more than 20% at best, if it does, that is.

Z77 chip set can run a single card at X16 speed, two card at X8/X8 and three cards at X8/X4/X4. The third option will hold the second and third cards back if they are of high bandwidth and require more than X4 to run at full potential.

Low profile and bandwidth cards could work tho and would be a good choice then. But that's not economical or worth it now. Maybe 5 years ago it could have been.