Please remember that any mention of competitors, hinting at competitors or offering to provide details of competitors will result in an account suspension. The full rules can be found under the 'Terms and Rules' link in the bottom right corner of your screen. Just don't mention competitors in any way, shape or form and you'll be OK.
A gtx780 would be no better and a stock 780ti maybe 15-20% faster. It's not really a question that can be answered correctly unless someone with a similar machine to yours and a 780/780ti runs it.
All depends how far that particular 780/ti overclocks. Most AiB 780's wil lhit reference ti speeds alright but its not guaranteed, But your 290 also has quite a bit if your lucky O/c potential in aswell so all in all for most games depending on which o/c's the most a 290=780 , 290x's/ti iirc add like 15-20% more
Even if someone had a more overclocked system I wonder would it be as much as 15%-20% difference with a 780Ti stock or overclocked.
Going by this video there does not look like much difference at all but then this is at 1440p :-
After watching that at 1100mhz on the 290 you are basically running around 780ti speed.
I agree with the thread, a 780 will make no difference, a 290X would add 2 FPS, a 780TI another 2 FPS.
The only way your going to get a substantial increase is by going Crossfire / SLI.
I will get some crossfire footage up similar to your video OP so you can see what extra a second card will offer you, minus the performance hit for recording of course though. I'm having trouble getting my recording software (Mirillis Action) to pick up my msi afterburner overlay though for some reason.
There does not seem to be any recording hit using Radeonpro.
Is there one while recording crossfire? That would be good to see crossfired 290 on the same level.