I'd go for the 1080 any day. The limited RAM on the 970 makes SLI not worth it IMO.

There is also power usage consideration.  The GTX 970 SLI will use about 300W max, 1080 will use 185W max.  If you game 4 hours a day, 30 days a week, its around an extra $2 in electricity a month, $24 a year.  So if you kept the 1080 for 4 years vs going with a lower cost 970, that lower cost 970 is actually going to cost you an additional $100 overtime in extra electricity.  If you live in a hot climate, the heat coming off the 970 SLI is going to add a bit to your AC electric bill as well.  At that point, you might as well go with the 1080 which cost more at time of purchase, but over the years you are going to save the money back.  (and its better for the environment) 
 
One more thing to point out, a new GTX 1080 purchased today is going to come with a 3 year warranty.  The 970's are likely passed their warranty and have quite a bit hours of usage in them already.  As an example, lets say a GTX 970/1080 will last 15,000 hours in heavy usage MTBF (mean time between failure)  and both 970's are at 5000 hours already.  That would be saying on average, most 970's are going to last an additional 10,000 hours, but statistically, especially with two of them, chances are one is going to go bad in the next 3000-5000 hours spent ingame (2-3years).  Statistically, it would be very bad to go into the 5000hr-10000hr usage area with 2 cards, one is uncomfortably likely to fail or have an issue. Edit: Keep in mind, those numbers are made up.  I can't imagine NVIDIA will ever list their cards expected life (MTBF).  But I can't imagine a GTX 970 lasting longer than 10 years on average, which is what I based it around.
 
Overall, I would highly recommend the 1080 or 1080ti and giving away the 970 to a family member, friend, or selling it off (your choice).

On heaven valley benchmark my score is 4119 everything maxed out on 1080p with overclocked settings max temp is 60c on top card bottom card is like 53c. Some guy was telling me that two 970s are way slower and hurting my performance. He has a 1080 and then started talking **** about my 2700x saying it was slower and he got 30 more fps then me and some other small stuff so i overclocked my CPU to 4.3 ghz with a score of 2006 on cinabench and he did the same with his 8700k at 5.0GHz with a Cinebench score of 1673
And my gtx score was higher then his I don't hate on other peoples setups idk why he came at me that way. I just wanted avg scores to see a wide range. That prick actually got to me sadly..