From Victron documents
100/30 Nominal PV power, 12 V 1a,b) 440 Watt
100/50 Nominal PV power, 12 V 1a,b) 700 Watt
150/60 Nominal PV power, 12 V 1a,b) 860 Watt
1a) If more PV power is connected, the controller will limit input power.
So if you choose the 100/50, you’ll miss ~100 Watt when...