Maximizing the efficiency and power density of dc-dc converters demands parallel optimizations in design and control, especially for variable-frequency converters operating over wide frequency ranges. This work presents the full-scale optimization of a kilowatt-range MHz-class boost converter based on impulse rectification. To maximize the heat extraction from the converter and increase its power density, the entire power stage is implemented on a single-layer insulated-metal substrate (IMS). For high efficiencies over wide frequency ranges, high-performance Gallium Nitride (GaN) transistors are employed and various high-frequency materials (MnZn, NiZn, air) with different geometries are compared to realize a wide-bandwidth inductor. Silicon Carbide (SiC) Schottky diodes with zero reverse recovery are utilized for efficient high-frequency rectification, and the impact of the device current rating on its generated reactive power and the overall system efficiency is investigated at different power levels up to 1 kW. A proposed optimum duty cycle control maximizes the conversion efficiency at different gains and powers and prevents fatal device hard switching at high frequencies. The optimized converter enables a peak efficiency of 98.6% along with an ultra-high power density of 52 kW/l (850 W/inch3). A loss breakdown summarizes major efficiency bottlenecks to be overcome by future advances in power electronics.