I don't need to i can show you results of a gtx980 being faster than a stock 980ti if you want in our own bench thread. If the stock gap was 40% this would not be possible.
102. Score 14491, GPU 980 @1560/2001, GFX Score 17185, Physics Score 13565, Combined Score 6991, CPU 4790k @4.9, faheemrazzaq, Post No.829 - Link Drivers 361.75
111. Score 13776, GPU 980 Ti @1000/1753, GFX Score 16521, Physics Score 11617, Combined Score 7004, CPU 4790k @4.4, savagesam117, Post No.348 - Link Drivers 353.30
This is the only stock 980ti in the thread.
This is the reason people think a RX 480 overclocked could possibly get close to a 980ti.
So when you overclock a 980 by 40% it is as fast as a 980Ti at stock. Interesting.