At 1080p? If that then that's frankly ancient... although I was playing 1440p with a 1070 a while back and was holding more than fine, but a while back and mostly limited by games being on consoles too and with settings tweaking which could be fine for some.
However now you'll have consoles that can eat that alive and hence ports won't really fare well on a 1070 or worst 1060 at all for obvious reasons, perhaps first year if a dev decide to develop a game for older and new gen as ram was similar.
EDIT:
Absolutely right just wrote same thing, new games won't be same games played for years as most games aren't really "pumped" for PC but have to work on both consoles and PCs so IMHO the 1080ti is the only 10xx that will still pull the weight from that series.