> a diode rated for higher current will also have more capacitance

In the datasheets for the MBR20100 and 100BGQ015 Schottkys
there is a plot for Junction Capacitance vs Reverse Voltage

For the first (20A, 100V), 600pF @ 0V to 50pF @ 60V-100V
For the second (100A, 15V), 5000pF @ 2V to 1000pF @ 15V

The datasheet for an MUR4020 (40A, 200V silicon ultrafast) shows

350pF @ 1V, 60pF @ 200V

> In fact, higher capacitance will likely slow dV/dt, which would
> then allow the circuit to tolerate a slower diode switching time
> before bad things happen

So the junction capacitance is a load imposed by the diode. As the
capacitance decreases, dV/dt increases, ie less load, faster switching

Getting back to my original question, with due consideration, two
20A Schottkys could be a substitute for one 40A ultrafast then

Joe

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