NefariousFraggle :
A few sites have done benchmarks on them. Just wondering how it compared to 1080 ti in SLI. If fewer games will be using SLI in the future then I'd go with the Titan. If not, 1080 ti. Tough decision...
I really don't understand what's making it such a tough decision. You realise that unless there's some big surprise going on here - which is extremely unlikely - the 1080ti and new Titan are based on identical GP102 GPUs. The only difference is that the 1080ti has 2 SMs disabled (of 30), a few less ROPs and a partially disabled memory controller. Again - identical GPU, just slightly cut down on the 1080ti.
At worst -
at absolute worst - then clock for clock the 1080ti is going to be maybe up to 10% behind the Titan Xp.
But, Titan Xp will be in Nvidia's blower design only, which is hotter, louder and can't boost as high consistently. A quality aftermarket 1080ti with proper cooling (like you're looking at) will consistently hit higher boost clocks than a Titan Xp on a blower cooler. So that
at worst 10% clock for clock deficit will be closed, maybe even surpassed at times, by the difference in clock speeds. Even if it doesn't fully close the gap, surely no one wants to pay $500 more for a hotter, louder card, just because they get maybe 5%, probably 2-3% extra FPS... that's crazy.
All the above, by the way, considers a single 1080ti vs a single Titan Xp. SLI 1080ti gets with a few % of the Titan Xp with absolutely no SLI scaling whatsoever. I agree with @Wildcard who suggests starting out with a single 1080ti and seeing whether you actually need the second.
Back when it was the 1080 (non ti) vs the 1st gen Pascal Titan X you could at least make a case for spending the extra on the Titan. At that time you were paying almost double for the 30-35% performance bump from the Titan. It wasn't good value, but at least there was a tangible performance edge to the Titan X.
Right now, there's just no reason to go the brand new Titan whatsoever.