AKICOLJ - PC upgrades

Quick question for those who know this sort of thing: what's a decent new graphics card to get?

LadyofAstolat wants to play the new Deus Ex, which says it needs at least a GeForce GTX660, or ideally a GTX970 (or equivalent).

Whereabouts are we on the tech curve with those?  Would a 970 be a good buy these days, or is the sweet spot somewhere up or down from there?