My G73 has trouble running SC2 on Ultra. I usually use medium/high details, but note I use 1920x1080P resolution whereas the one you listed has a 1600x900 resolution.
In large SC2 games (8 players)- my computer does slow down a bit in heavy action - dipping below 30FPS.
But also note that a lot of computer have trouble running SC2 on Ultra at 1080P unless you have a serious desktop/DTR.
Diablo 3 - well thats a bit harder to say. I'm guessing it will be less taxing on yout CPU and GPU than SC2. So you should be able to get at least high detail in D3.