Speed and memory
In our performance index the Radeon R9 285 scores 6 and the GeForce GTX 680 scores 5.5, which makes the Radeon R9 285 about 9% faster. That is a small gap, below what most people notice without a frame counter.
Both cards have 2 GB of video memory, so memory will not separate them.
In our estimates for popular games at 1080p on High, the biggest gap is in Cyberpunk 2077 (10 against 9 fps), and the smallest is in ELDEN RING (15 against 14 fps). Games that are light enough to run above 200 fps on both cards show little difference at all.