The TPS92511 is limited to 500mA, but that's probably enough, as it's never a good idea to drive LEDs at the maximum current.
The MP4700 will need a lower voltage supply, just like my LM358 op-amp suggestion, but that's not a problem, as you can just use whatever is powering the boost converter.
A buck converter will be theoretically more efficient, than a linear regulator, but bear in mind, if the output voltage of the boost converter is only a few volts above the forward voltage of the LEDs, it might not gain you much. Suppose VF = 37.5V and VIN = 40V then the efficiency of a linear regulator is 37.5/40 = nearly 94%.