Speed and memory
In our performance index the Radeon R9 280 scores 4.5 and the GeForce GTX 660 Ti scores 4.2, which makes the Radeon R9 280 about 7% faster. That is a small gap, below what most people notice without a frame counter.
The Radeon R9 280 has 3 GB of video memory and the GeForce GTX 660 Ti has 2 GB. That difference matters at 1440p and in new games at High textures, and it can outweigh a small speed advantage as the card ages.
In our estimates for popular games at 1080p on High, the biggest gap is in Red Dead Redemption 2 (13 against 10 fps), and the smallest is in Grand Theft Auto V Legacy (75 against 71 fps). Games that are light enough to run above 200 fps on both cards show little difference at all.