I think you'd have to take that statement with a grain of salt, especially coming direct from nVidia, and I'm guessing that if the stars aligned in a perfectly coded application designed to use every ounce of power from the GPUs that you might see 10x the performance, but I highly doubt that'll ever happen in the games that we play (although it'd be so nice to be wrong).
I would have to guess that 8-way SLI is going to be something special for workstations or supercomputers, or something else along those lines. I don't think they're expecting gamers to be taking advantage of it, at least not at first, and I don't think any modern day motherboard has the capability to do > 4-way SLI if it was even an option.
I'll agree that it is an odd rumor, and the original rumor was that it'd actually be a cut down GM200 chip. So, slightly slower than the Titan X with half as much VRAM, but I'm all for it if nVidia wants to enable more CUDA cores in the Ti version and sell it for less than the Titan X.
It might be time for a full case upgrade with (possibly) water-cooling, so I'm pretty excited to be thinking about all of that.
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