I have a current Mac Pro with a ATi Radeon HD 4870, and now I would like to add a third monitor. Now, a friend of mine had some weird problems when adding a second 8800GT to the previous generation Mac Pro -- remember, the nVidia 8800GT was the "better" option for that machine, and the Apple Store website would only give the option of just one nVidia 8800GT. (Or up to 3 or 4 ATi 2600XTs.) The machine would boot and all, but Final Cut Pro would crash when rendering. The solution was a downgrade to 2xATi 2600XT. The current situation is of course much the same: one can order multiple nVidia GT 120s or one ATi 4870. I am not going to try to add a second 4870 to my system, given my friend's experience with two "better" videocards. But I would like to add an nVidia GT 120 for this third monitor I'd like to add. Does anyone have experience with this? Will this work okay? And: is this risky in terms of OpenCL, i.e. is it possible that OpenCL gets confused as to what graphics card to use? That maybe, in a worst-case scenario, OpenCL is shut off altogether?