with the classy i have performance near the same levels, Many people said that swapping will be a down grade (780 it self) but to be honest this has (w/o overclocking) at least 10% more performance to a reference 780. once you over clock you get some extra juice out of it so you are almost on par (FPS wise) with a 780ti reference.
In the long run in my personal opinion if i had to chose between this and a 290x, which are in the exact same price range with MSRP, after they reset to their original value, which will be soon, I will pick this card 10 times over.
Here are facts that I do notice even if you have a stable 290/290x
Software wise:
1- If you over do the OC you just get a driver crash versus a black screen with 290/290x.
2- If for example you have "apply Oc at windows startup" with 290/290x and is a overdue clock, good luck its a living nightmare to get your pc to work (the first time around I ended up re-imaging, the second time it took me 2 hours).
3- Geforce experience >>> AMD combat evolve.
4- I was lacking good Xfire support in AMD for over 4 months I was not able to use my cards in crossfire while using my headset it will sound stutter, if i used headset then it will disable all usb ports.... This was fixed in the second mantle patch
5- overall being able to press your macro to record the last "X" seconds of your gameplay is amazing, I don't stream, and AMD Radeon pro is decent for amd, but when you do a WTF moment or some one in your party says something amazing or does something stupid tyou could always go back.
Hardware wise:
1- The noise level. The 780 classy is so silent that after 3-4 months I finally notice my PSU had a failure (squeeking/buzzing sound).... LOL over all this card is so silent that the system makes similar sound with air cooling than with a 360mm rad shared between this and CPU (with no overclock in neither) .
2- Heat level, 95 degrees vs not even hitting 70..... yeah that helps the case and my life as a whole lol.
now that they are releasing the 6gb version theres really no reason why not to get a 780 over a 290x.
or just wait for maxwell at end of year i guess