Alright then, these are the facts. With 3-way SLI the more 'dated' games will run into that dreaded CPU bottleneck fairly fast unless you really make it heavy on the GPUs, that means resolutions of 1920x1200 and above and flicking on everything you can image quality wise. With the more GPU limited titles like Metro 2033, Battlefield BC2, Crysis and even Far Cry 2 with say 8xAA 3-way SLI does show noticeable gains. But as stated you do need to seek it at the extremely high resolutions.
On the topic of high-resolutions, there are more situations where you can reap the benefits of multi-GPU modes. 3D stereoscopic gaming for example with a modern title can cut your framerate in half. Also, gaming with three monitors where you literally increase the GPU load by threefold, these are situations where a setup like shown today makes sense.
What doesn't make sense obviously is the massive amount of money you need to spend on a setup like this :) The three cards alone will set you down roughly 1400 EUR, and then you still need to build a PC around it. Make no mistake, you'll need heavy duty gear. A top of the line 3-way SLI compatible motherboard, a nice overclockable processor, as you really want some more processor performance, and then obviously we need to have a chat about power consumption and your power supply. The very bare minimum you'll need to get is a kilowatt PSU, and you'll need quality of course. In the worst case scenario with the GPUs overclocked and our processor running at 3.8 GHz we here and there touched 950W (!). So we say, get yourself a good 1200 Watt PSU, and make darn sure that the PSU you choose has these 6-pin AND three 8-pin PCIE PEG connectors to feed the graphics cards.
When it comes to CPU bottlenecking you might wonder... why not overclock that processor any higher? Well, with the complexity of three GPUs you need to find yourself a stable symbiosis of components. We could say overclock to 4.4 GHz yet would need to alter CPU cooling to LCS or better and that PSU would need to be rated higher as well. Remember, overclocking requires additional voltage on the processor, if you need to step from 1.3v towards 1.5v or even higher your overall peak power consumption will rise significantly. An additional 100 to 200 Watts would not be weird at all. And that's why we kept the processor at our 1.35v / 3.75 GHz sweetspot as overclocking it dramatically higher would endanger system stability by pushing the 1200 Watt PSU close to its limits.
So then, in conclusion as always, this is x-factor stuff, extreme, nearly silly stuff to do and show. But people out there do purchase setups like shown today. At least you now know the pros and cons. Our recommendation is simple, if you have the hots for a multi-GPU setup based on the GeForce GTX 580, we recommend a 2-way SLI setup at best. With 3-way you'll run into heaps of curiosities like power consumption, noise levels and then the CPU bottlenecks - that last one is just sheer dreadful.
Flipside of the coin, 3-way SLI can be really helpful with 3D Stereoscopic gaming and a triple monitor gaming setup. The drivers, as always, are done well, we did not have any issues significant enough to mention, so from NVIDIA's side it's all good. But on a single monitor we do think that the infrastructure and sheer cash needed outweighs the extra performance you'll get for it in return. But that doesn't mean it's not tremendously cool stuff to play around with though.
Oh and 4-way SLI you wonder? Worse... that's 2-3% performance increase if you are lucky, with 3DMark Vantage as the exception. So yeah, stick to 2-way SLI we say -- unless you need to break 3DMark records of course :)
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