The new Maxwell cards are amazing and also come with some new features you should read about if still on the fence. Here's the Asus performance as I don't have a good average of games for the MSI card (just increase it even more in the charts): http://www.techpowerup.com/reviews/ASUS/GTX_970_STRIX_OC/25.html
So the MSI GTX970 is at least 15% faster than an R9-290X if you compare overclocked cards.