Year 2009+ Model 5,1: (our rating score out of 10)
ATI Radeon 5770 1GB (4/10) - minimal performance. no CUDA. This card is fine for daily tasks and audio production, but not sufficient for video editing.
ATI Radeon 5870 1GB (5/10) - even though it's also 1GB, it has a more powerful internal processor than the 5770. But still, no CUDA. This card is fine for photography. Photoshop requires performance, but not as much as video editing.
GTX 680 2GB (6/10) - Compatible with Mountain Lion 10.8 and Mavericks 10.9. Strong internal processor. 1500 CUDA cores. Very popular card because nice performance at fair price and pretty quiet.
GTX 780 3GB (7/10) - Compatible with Mountain Lion 10.8 and Mavericks 10.9. Very high performance. 2300 CUDA cores. Higher performing than the GTX 970. Maybe 15% less performance than the 980Ti at about half the cost. See here for comparison between GTX 780 and 980Ti.
GTX 970 4GB - (6/10) - Latest generation. Requires the NVIDIA driver which requires Yosemite 10.10 or newer operating system. The base model of the latest generation. 1500 CUDA cores. Good performance. The GTX 780 3GB is actually higher performing than the 970, but the 970 is more power efficient and a bit quieter.
GTX 980Ti 6GB - (8/10) - Latest generation. Requires the NVIDIA driver which requires Yosemite 10.10 or newer operating system. Very strong internal processor. 2800 CUDA cores. Second to best. The difference in performance between the 980Ti and Titan X is not much, maybe 20%. See here.
GTX Titan X 12GB (10/10) - Latest generation. Requires the NVIDIA driver which requires Yosemite 10.10 or newer operating system. Very strong internal processor. 3000 CUDA cores. The best.