Gaming performance is just a part of determining how fast each graphics card is.
In 3DMark test we are only comparing GPU scores. While the GTX 780 Ti and R9 290X are far ahead of the competition, R9 285, GTX 770 and R9 280X are quite close to each other. Radeon R9 285 was of course faster than R9 280, however it remains unable to come close to R9 280X in non-Extreme Fire Strike test. Once we move to Extreme test, the difference is few and far between.
I found it rather surprising that GeForce GTX 780 Ti managed to score 40% more than R9 290X. Radeon R9 285 was the slowest card in 1440p benchmark. I think it’s quite obvious that Catzilla seems to favor NVIDIA hardware. There is no reason why GTX 760 would perform better than R9 280X.
CompuBench is a OpenCL benchmark. Before 2nd Gen. Maxwell AMD had no trouble beating the competition. Both R9 290X and R9 280X are doing very good against GTX 780 Ti.