There are no fastest 1080 Ti cards out there, other than the reference (and maybe MSI Armor) all 1080 Ti perform ~ the same. Pascal cards don't overclock nearly as much as the previous gen, and countless tests showed that it doesn't matter which card you buy as long as the cooling is good. It's all down to the silicon lottery, the most basic cheap 1080 Ti can get to a higher clock/voltage pair than the most expensive one if it happens to receive a better chip (which is random for the most part). Not only all those extra phases don't help with overclocking (since nvidia has nerfed it at some very moderate level), none of it really matters for mining where you tune the card for some kind of optimal hash/watt/$ ratio and I don't think there's many miners out there that run their Ti's at stock or higher than stock voltage. No one runs their 1080 Ti cards just the way they are out of the box (except total noobs, I guess), so the stock clocks just don't matter.