NVIDIA GeForce GTX 680M 's Advantages
Boost Clock758MHz
More VRAM (4GB vs 2GB)
320 additional rendering cores
AMD Radeon R9 M390 Mac Edition 's Advantages
Released 2 years and 11 months late
Larger VRAM bandwidth (174.7GB/s vs 115.2GB/s)
Lower TDP (80W vs 100W)