Far Cry 3 features heavy tessellation, high amounts of volumetric lighting, and deferred radiance transfer volumes (global illumination). This is because the game is running on the Dunia 2 Engine, a modified version of Crytek's CryEngine.
Running on IO Interactive's proprietary Glacier2 engine, Hitman: Absolution is a challenging benchmark. It features a very hardware intensive engine that is able to render up to 1200 NPCs simultaneously. The benchmark tool used to test this game is extremely intensive, besides the massive crowd of NPCs, it also features Reflective Shadow Mapping (RSM), Direct Compute accelerated Bokeh Depth of Field, extreme tessellation and Ambient Occlusion.
From the results of these in-game benchmarking tools, the ASUS Radeon R9 280X turned in a mix performance. For Far Cry 3, it was consistently trailing the GTX 770 but its managed to outperformed the older Radeon HD 7970 card. For the Hitman Absolution test, it beat the GTX 770 when the game's anti-aliasing feature was turned off; however, with the feature enabled, the ASUS card failed to show the benefits of its improved GCN-based R9 280X GPU. Generally, It didn't performed as expected when anti-aliasing was turned on; however, we suspect that with newer drivers for the AMD "Hawaii" cards, they would turn in better performances. We'll have to re-assess performance in the near future to see how it might improve with mature drivers. The good thing is that the R9 280X is consistently beating the GeForce GTX 760 which AMD compares itself against (though note that price points are different for both products).