I own an Acer Predator X34 (3440x1440p) g-sync monitor. In order to utilize this resolution, the GTX 1080 is a perfect match. The GTX 1070 could likely output 60 frames a second @ that resolution, however settings would likely have to be dialed down.
I am not a user who needs max settings across the board, but when you consider the price of g-sync monitors it seems foolish to then become budget conscious when considering your GPU. It be like buying 4K TV, and then buying a standard Blu-ray player because the 4K Blu-ray player is too expensive. I'm not suggesting to buy a Titan X, but $200 more for the 1080 vs the 1070 is well worth it, again assuming you are playing @ 3440x1440p.
To be honest, I used the 1070 for a day, and was underwhelmed by it's performance in comparison to my previous GPU, a GTX 970, on a standard 16:9 1080p monitor. However, this isn't a fair comparison, as I only used it for one day and one game, GTAV.
EVGA SC was an easy choice considering, with price match was less expensive, and benchmarks showed it kept cooler temperatures than the reference 1080. After a few weeks of use I can confirm that to be true. Almost all non-reference cards appear to out perform the Founder's edition, and the difference in performance amongst non-reference cards appears minimal.
I should also mention that purchasing through BestBuy for something like this was a much better experience than ordering online. There were several reasons:
1) I originally purchased the GTX 1070, and was able to return it, hassle free, the next day. Had I purchased online it would not have been that simple. Customer service @ the Lafayette, IN store is top notch.
2) I prefer BestBuy's extended warranty to anywhere else. If I have a problem with my monitor, I can take it right to BestBuy, as opposed to having to mail it in. I've also heard fewer stories of BestBuy shying away from warranty coverage vs many electronic retailers.
3) I can only speak for the Lafayette, IN store, but they made the whole process easy. I was able to price match without issue, and get exactly what I wanted. I didn't have to speak to someone on the phone reading from a script that I couldn't understand.
The PC sales staff were enjoyable to talk with, and knew what they were talking about. The GM in particular went out of his way to ensure I was able to get the monitor I wanted, the Acer Predator X34, and it's incredible. If you're not using g-sync, or free-sync (depending on your card), you should be.
4) BestBuy Credit Card w/ special financing on all this? Yeah... no question.
All the best