There's always going to be something better down the line-what you need to determine is does the card suit your needs? Are you planing to play games at 1080p or hoping to game at 4k or even VR later down the track? Are you happy dropping a few settings down a notch or are you one of those people that needs everything maxed out?
Getting a 970 for that price is a steal-it's a great card that will remain relevant for a while to come. Yes, of course, a 980ti is significantly better but it's also significantly more expensive. As far as polaris/pascal cards are concerned there really is no solid info on them-yes everyone is expecting them to be great but i imagine they will be priced accordingly as well costing an arm and a leg.