I actually just upgraded from a 7850 to a 770. Based off the games I play most (which is like LoL, Sc2, D3, and some rpgs from steam), I can tell no significant difference. Granted a majority of those games aren't tooo demanding, and I would definitely see the difference in more demanding games. So if you're unhappy with your performance in the games you're currently playing (you want higher settings, or higher fps) go ahead an upgrade. If not, I think it would be better to wait until you see a drop in performance to buy.
The 290 is better than the 770, and both are better than the 7850. I'm not too sure about prices in EU (from the US), but just go with whatever fits your budget.