The solution size is smaller with higher switching frequency; the efficiency is higher with lower switching frequency. But we should also consider the minimum switch on-time of the converter when choosing the switching frequency. The minimum controllable switch on-time of MAXM17552 is 152ns, according to formula, ton(min)=Vo/Vin(max)*fsw, assume Vin(max)=55V in your design, then ton(min)=4V/55V*450kHz=162ns. So 450kHz is okay for the design.