varistor - MOV Characteristics

I need to select MOV for my application. Vin max=520Vrms Surge Voltage= 4000KV as per IEC61000-4-5, 8x20us waveforms.

So my calculation is $$ \text{Surge Current}={(V_{transient\_max}-V_{clamp}) \over Z_{source}} = {(4000V-1500V) \over 2\Omega}=1250A$$ $$ \text{Energy}=V_{clamp} \times I_{surge} \times T_{pulse} = 1500V \times 1250A \times 20\mu s = 37.5J$$ $$\text{Power}=\text{Energy} \times \text{cycle}=37.586s=0.625W$$

So I Selected the above Part No. And I hope this will work, but in datasheet two more graph are there , dont know how to use those two graph , if they are impacting me to select the MOV. (image attached)