GTX 780 outperforms R9 290 & performs on the par with R9 290x, so GTX 780 Ti will easily beat R9 290x.
Though there is big price difference between 780Ti & R9 290x, if budget is not the issue then GTX 780 Ti is the way to go for current & to-be released games otherwise R9 290x won't let you down and is a great card for its price range.