I'm stuck on deciding between the Mac Pro and purchasing the Nvidia GeForce GTX 285 Mac edition or purchasing an iMac 27" i5 with an ATI Radeon HD 4850 for playing games at 2560x1440 resolution.
From anyone's experience or knowledge does the ATI card hold good frame rates at a high quality setting in most games at this resolution or does the 285 blow it out of the water and warrant the extra cost of the Mac Pro plus 30" screen.
You might try asking this question in the "Graphics & Displays" forum without mentioning the Mac computer. You'll reach a lot more gamers with experience testing various GPU cards against each other.
A GTX 285 is MUCH more powerful than a 4850, but that shouldnt be your primary concern in this decision(see below). The 4850 is a good card, and would play most games at medium-high resolution--but probably not with the best framerates or with all options turned on.
The biggest concern is that the imac does not have room to upgrade any of its components, while the Mac Pro would have room. This is my big concern about the 4850--its already an older card, and you probably wouldnt be able to replace it on the imac.
Overall, this is a very odd question because not many people use Macs for primarily gaming. (I own both Mac and PC--so I can say this as an unbiased observer)
Apple kind of has a weak spot in their lineup at this range--because the Mac Pros are very expensive and intended to be extremely high powered workstations, while the iMac is intended to be a basic home computer with little option to upgrade.
I should also note that Macs are generally not good gaming computers because of the number of programs available. Even with the Mac resurgence in popularity only a fraction of PC games are released on Mac. Also.. you can customize a new PC for far less than the purchase price of an iMac. Typically people buy macs because they want computers that are easy to use, high quality, and simple--and they pay twice as much for that luxury.