Which 1080 ti is best?

Solution
the manufacturer applied OC settings will not damage the GPU

They are well within tolerable limits

Nvidia recommend a 600W PSU for the 1080ti and a Strix will require 2 x 8pin psu connectors
as far as 'in game' performance, they're all pretty much the same.

the main difference is their factory set OC settings and the cooling/noise performance.

I've always gone for the Asus Strix line as it's still one of the best performing GPU air coolers on the market

EVGA are also very popular and have some of the best customer care service.
 
the difference between all the aftermarket 1080ti GPUs in minimal as far as FPS goes.

Out of the box, pretty much all of them will perform the same as each other.

As far as the Strix line goes, technically the best one is the OC version as it comes with higher stock clock speeds, so it effectively performs better out of the box

https://www.asus.com/uk/Graphics-Cards/ROG-STRIX-GTX1080TI-O11G-GAMING/