NVIDIA Quadro K3100M 's Advantages
More VRAM (4GB vs 2GB)
Larger VRAM bandwidth (102.4GB/s vs 80.19GB/s)
256 additional rendering cores
NVIDIA Quadro M620 Mobile 's Advantages
Released 3 years and 6 months late
Boost Clock977MHz
Lower TDP (30W vs 75W)