There you go. Magsafe can only provide 85 Watts by design. GPU is just throttling to meet the power draw since exceeding it will result to battery drain while being plugged in. 3D mark does not max out both CPU and GPU at the same time unlike GTA V so you see heavily throttling there. Just switch to iGPU for consistent FPS since the power consumption will be reduced to 47- 60 W which Magsafe can easily provide.