AMD Radeon RX 490 and the Geforce GTX 1080Ti are on the top of rumors these days and also the most awaited upcoming chips. So for the game lovers, this is the really impatient phase. Regarding Radeon, it is 2 nm smaller than the GeForce GTX 1080 Ti. So this means it is expected to work very slightly cooler and achieve higher clock frequencies than the GeForce GTX 1080Ti.
The Radeon RX 490 requires 225 Watts to run, in contrast to GeForce GTX 1080Ti that requires 180 Watts. For Radeon RX 490 it is recommended to have a 550 watt PSU and for GTX 1080Ti it is recommended to have a 500 watt PSU. This difference can be considered quite significant as well, since the results may reflect on your electric bills.
If both of these GPUs are compared it can be seen that both of them have the same amount of video memory. But they can provide little bit different experiences when the game is played with high textures at high resolutions. The RX 490 has 703.7GB/sec greater memory than the GeForce GTX 1080 Ti which shows that the memory performances of the RX 490 are mostly better than the Ge Force GTX 1080Ti.
Talking about processors, Radeon has 40906 Shader Processing Units and GeForce has 2560. However, the actual shader performance of the RX 490 is 4301 and of GeForce is 5989. Similarly, the GeForce GTX 1080 has a 557 MHz higher core clock speed than the RX 490 but the RX 490 has 96 more Texture. The RX 490 has not been released yet, so any comparisons may not be too reliable.
It is said that AMD Radeon RX 490 is arriving as soon as next month while the GTX 1080 Ti has an expected early 2017 launch. So pricing is unavailable at this point.