It would be 2*fe 1080s
So clocked at around 1800 by default
What would be two FE's? The comparison I provided was against EVGA GeForce GTX 1080 FTW which are 1860MHz boost (what they would run at).
The FE are clocked at 1733MHz boost.
What wasn't mentioned is the comparision of a manual overclocked 1080 vs manual overclocked TXP.
That works out at as:
54fps for the manual OC 1080
67fps for the manual OC TXP
so percentage wise you would gain 24% fps from moving up from the 1080 to TXP at twice the price so that is a large diminishing return in my opinion. But then if you took the 1080 in SLI at the same price then you would end with it looking like this
50fps for stock OC 1080
(different 1080 card as what I can find to compare Palit Gamerock Premium compared to EVGA FTW)
54fps for manual OC 1080
67fps for the manual OC TXP
82fps for the sli stock OC 1080
No manual overclock given for the cards but even on the basis that you can place two then yes the 1080 in SLI is the clear winner for Witcher 3.
(All figures in last example for for 4k gaming however with hairworks off for all also).
Now in the interest and because of cost. 1070 SLI for witcher 3 actually gave 68fps
If the other games you play are;
Assassins Creed Unity
Crysis 3
The division (least optimised lowest fps regardless of card)
farcry primal (assume all farcry series would be similar as same engine)
rise of the tomb raider
Then actually the 1080 in sli make sense, heck in all of those titles 1070 sli actually beat out the TXP at 4K so you would have the same performance at a much lower cost.
The low of 52fps for The Division and however the TXP only manages 50fps also. Now you could go down the watercooling route for the 1070's to try and gain a little more with a decent manual clock and still be under the budget of the TXP.
The problem is for a lot of other games as stated the SLI doesn't work and so you drop back down to 30-40fps for a 1070 then at 4k.
If you decided that is too much of a drop and a hassle a 2nd 1080 in the games listed above provide around a 30% increase over the TXP. That to me is reasonably healthy considering costs. Again it would depend I think on your total games collection on what you do.
Witcher 3 and/or any of the above go for a 1070/1080 SLI for most others the TXP works out better.