atomicWAR :
even at 1080P some games won't do it or in turn require SLI (if supported). I see reviews all the time saying SLI is overkill at 1080P. I
SLi does wonderful things with the 970s (70% average FPS increase, 95% in the more demanding AA games). However that average drops to only 18% at 1080p and 33% at 1440p. This is the 1080 but scaling is usually consistent across the x70 and x80 cards
https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_SLI/20.html
That's probably a combination of...
a) The 10xx is about 100% faster as the 9xx .. but the % difference between the 6700k and the 4790k are in single digits
b) Be a while before nVidia is able to catch up w/ DX12 scaling and DX12 scores are what's bringing average down
c) It's not in nVidias interests to improve scaling on 10xx series cards. With no competition from AMD in this performance niche, improving the 1070s SLI performance would have only 1 impact... it would gut sales of the 1080 and they make more money of one 1080 than two 1070s
With the 1070 you are good to go in 1440p/60FPS OR 1080p/120-144FPS
Just to clarify going from 1440p to 1080p also won't double frame rates... 35 - 75% is typical. Son No. 2 has twin MSI 970s gaming w/ 20% OC) on 1440p Predator monitor @ 144 Hz and he hasn't dipped below 60 fps in anything he's played yet. In Witcher 3, as I recall he's about 76 fps w/ the OC ... the 1070 managed 60.7 fps in W3 .. should hit 70+ with an OC'd MSI 1070 Gaming. Note that W3 is one of the few games where 970s in SLI beat the 1070, the 1070 wins in most games against twin 970s.
But, this is a lappie and the 1070m doesn't quite keep up with the 1070, tho it's much better than what we were accustomed to in previous generations.
https://www.youtube.com/watch?v=k9TwndWcvM4
http://gpu.userbenchmark.com/Compare/Nvidia-GTX-1070-Mobile-vs-Nvidia-GTX-1070/m164129vs3609
http://www.tomshardware.com/news/nvidia-geforce-gtx1070-mobile-pascal,32481.html
Mirrors Edge - 102 / 92
Hitman - 75 / 63
Witcher 3 - 65 / 57
Need 4 Speed - 98 / 85
Gotta note that just Cause was a lot faster on the lappie in that youtuber's test but can't account for that. You'll see fps in the 40s in some games with a 1070 (desktop) maybe a hair under 40 (lappie) in those at 1440p. But frankly, the 1070 is a superb card at 1440p and can even be called "too much card" for 1080p in either desktop or laptop configs ... I expect you might find 1 or 2 games to go under 60 fps with the laptop version, but it won't be by much.