Obviously there's no such thing as futureproof, as not one of us knows what the future will bring. Also, some more information is really needed to be able to offer much advice, such as what resolution you play at? Do you think you'll still be playing at the same resolution in 5 years time?
It's worth keeping in mind that different people have different opinions on what is acceptable performance; for some it has to be minimum 60 FPS, while for others, it's anything over 30 FPS that's fine. This distinction matters, as even now a 780 can't keep above 60 FPS maxed out in a few games (Crysis 3 for example), so how bad do you think it'll be in 5 years time?