Yea, having a huge monitor can be problems with getting super good graphics in games. We bought our computer like a year ago, and it cost $1300 I think (we tried other methods to get a cheap one, but ended up getting a faulty computer, so just went and bought one in a store). Its got an older quad core, (9650 I think), and 1 gb 4650 graphics card. Strange enough, they bundled with it a 27" 1920x1080 screen. (just to clarify, its not a mac, but the same general idea results). The massive screen is sweet for doing pretty much everything, including gaming, but since I have my games set to a 1920x1080 resolution, I'm only able to run smoothly on like medium.
Money can't buy happiness. Just video games, which make me happy.