http://www.techpowerup.com/reviews/ASUS/GTX_970_STRIX_OC/25.html
1) *GTX970 and GTX780Ti are nearly IDENTICAL once overclocked as the 970 is only a bit behind at stock but overclocks better.
2) GTX970 runs much quieter (most models can turn fans off during light/medium usage)
3) GTX970 can run MFAA for supported titles (alternate to MSAA which can boost frame rate a bit)
4) GTX970 has a NEWER ARCHITECTURE which will begin to benefit newer titles more once they optimize towards it.
5) GTX970 has other features such as:
a) H.265 as well as H.264 encode
b) HDMI-> 60FPS @4K
c) HUD optimizations
d) Voxel lighting support (future games)
Summary:
On AVERAGE the cards are only 2% apart at 1080p/1440p and when overclocked the GTX970 will...