n00b!3 SLI and Scaling Questions

Firstly, what does scaling mean?

Whenever I mention a triple or quad SLI setup, someone has to say they would never do it as it doesn't scale well. What is scale? all benchmarks show the more GPUs the higher the score

Secondly, again, why do some say the best setup is a dual SLI not more?

 

Scaling is how much performance each additional GPU adds over the baseline performance of a single GPU.

Hypothetical scenario with perfect scaling:

1 GPU = 20 FPS
2 GPUs = 40 FPS
3 GPUs = 60 FPS
4 GPUs = 80 FPS

Each additional GPU adds +100% (+20 FPS in this case) over a single GPU.

Of course, it doesn't always work out that well in the real world. To take the example above, in reality you might be looking at:

1 GPU = 20 FPS
2 GPUs = 40 FPS
3 GPUs = 50 FPS
4 GPUs = 55 FPS

So you see how the point of diminishing returns kicks in after 2 GPUs. You're paying a hefty sum for the 3rd and 4th GPUs but not getting anywhere near +20 FPS each time. With some overclocking you could probably come close to matching the performance of 4-way SLI with 2-way, saving yourself half the money in the process.

Your ROI decreases progressively as you add more GPUs. This is why 2-way SLI is recommended over 3-way and 4-way, and why 1 GPU is king if you want guaranteed performance.

Poor scaling can be the result of CPU bottlenecking, suboptimal SLI profile, bad SLI support in the game itself, or any combination thereof. Adding more GPUs exacerbates these problems.

 

noone could have explained it in a more clear and concise way! I really appreciate it!

+Rep given