If you are going to SLI 2 ACX style cards with 0 slot spacing, make sure that you have PLENTY of air flow.
 
The top card will be starved for air by the bottom card.
 
You should consider the hybrid cards...as long as you have space for 2 120 mm radiators.  They will run cool with 0 slot spacing.
 
Any reason why you want to SLI 2 $450 cards = $900?  If you are going to spend that much, it might just be better to get a Titan X P for $1200.  Less power, better scalability (not all titles scale properly with SLI), and no SLI issues.

In that case, you should get the hybrid card...and make it your top card in the SLI stack.
 
Also - you can buy the EVGA hybrid kit for the 1070 FTW...and have 2 hybrid cards.  The modification is not hard...just take your time.  It will take you about an hour or so to modify.
 
I did SLI about a year ago...don't do it anymore...
 
I have 2 Titan X P and 1 1080 FTW.  (all fold 24/7 when not gaming...I do not SLI the Titans).  I have replaced the air cooling with the EVGA 1080 hybrid kit (kept the Titan X P PCB heatspreader and backplate, used the AIO instead of the heat fins)...the temps on the Titans went from 84 C under load (at 100% hair dryer fan speeds) to sub 50 C under load (and almost dead silent).
 
Good luck...and keep us posted!

Do I think it will improve in the future?  That's hard to say.
 
SLI support for a game requires that the developers do extra coding to support SLI, and that the drivers support as well.
 
Many of the popular "main stream" games support SLI.  Just Google it and make your call based on how you feel.  At the end of the day, your worst case scenario is that you will have to disable SLI in the NVIDIA control panel to run certain games.
 
If you are going to have that extra GPU horsepower, consider the folding @ home project.  It's a great cause!
 
As far as my avatar...I have an equally offending one for the other side...I might update after the results of tomorrow's election - hehe.

I purchased a 1080 FTW first as my planned upgrade.
 
Then I started reading about the Titan X P...purchased it on a whim.
 
The Titan X P is fabulous!  I thought the 1080 FTW was fast...the Titan X P is like...WOWOWOW fast.  Both of my Titans overclock to 2075 MHz for the GPU...just fabulous!

Holdan
Hello everyone,
 
I'm planning to sli two gtx1070 ftw cards on a Asus maximus 8 gene mb, all within a Thermaltake core v21 case. I would like to use the high bandwidth evga pro sli bridge but not sure which slot size to get. Do I need to get the 0-slot sli bridge or the 1-slot?
 
Many Thanks.
 
Edit: I've found out which sli bridge needed, it is the 0 slot (short) pro. 

Just to confirm your findings, yes, that would be the correct bridge for SLI on your mobo..Just remember that PCI-SIG/Industry standard specs dictate that every 20mm (20.32mm to be exact) is counted as a PCIe/PCI slot space whether there's a slot there or not..The 40mm bridge is what you need and as long as your PSU is sufficient you'll be good to go.