The Qualcomm Snapdragon 720G integrates 2 ARM Cortex-A76 Gold Cores ticking at 2.30GHz and 4 Cortex-A55 Silver Cores at 1.80GHz while the Snapdragon 845 has 4 ARM Cortex-A75 Gold Cores that can be operated at up to 2.80GHz clock speed and 4 Cortex-A55 Silver Cores at 1.70GHz clock speed.
Here the SD 845 has a better clock speed but the SD 720G has a better CPU architecture so the SD 720G has a slightly better CPU processing in comparison to the SD 845.
GPU-wise, the Snapdragon 845 is ahead, because where the Snapdragon 720G has the Adreno 618 GPU whereas the Snapdragon 845 features the Adreno 630 GPU. So in terms of gaming, the flagship Snapdragon 845 is still better than the mid-range Snapdragon 720G.
In this section of power-efficiency, the Snapdragon 720G is better than the Snapdragon 845 because where the Snapdragon 845 is fabricated on Samsung’s 10nm 10LPP Process technology whereas the Snapdragon 720G is built using 8nm Process technology. So in terms of power-efficiency, the Snapdragon 720G is better than the Snapdragon 845.