The company claims you can play ULTRA with a GTX760 though they don't specify the frame rate. I suspect they mean at least 30FPS because I've seen game footage and highly doubt you'd get 60FPS. They also didn't specify RESOLUTION and while I personally think that should mean 1920x1080, it may not.
At 1366x768 you'd get a higher frame rate, but the R7-250 is also a lower-end card. I'm roughly guessing about HALF the performance of a GTX760.
*So, at 1366x768 you should have a great experience, but it would be a very bad idea to just crank up to ULTRA settings. You should carefully tweak the quality settings to achieve your desired frame rate (i.e. 40FPS average with VSYNC OFF, or VSYNC ON at 60FPS).
I recommend 40FPS with VSYNC OFF if the screen tearing isn't too bad. VSYNC ON requires you to stay above the target refresh of 60FPS or else you get stuttering.
I use Adaptive VSYNC and usually tweak games to run above 60FPS 90% of the time (get screen tearing when it drops below 60FPS but it's better than the stutter issues). I think RadeonPro may have a similar feature now but I don't think AMD has this yet though they really should. It's great if used correctly.