In our never-ending search for an imac replacement (cannot afford a new one), we have found a 2013 with a GTX 775M. I do not know how this compares to an AMD Radeon? It needs to run Trainz A New Era which requires NVIDIA GTX 660 or better/ AMD HD 6950...(and I am guessing being a 775, it fits the bill). BUT, I understand this is a chip? If this sucker goes out, that would be a replacement of an entire motherboard? It's not a simple "pop it out and replace it"?