Epitaxial beta-SiC films have been successfully grown on Si(100) at substrate temperatures considerably lower than those used during conventional CVD growth. This has been achieved using translationally energetic and spatially directed methylsilane delivered via seeded supersonic molecular beams. Methylsilane kinetic energy was found to dramatically affect both film morphology and growth behavior, as well as the enhancement of growth efficiency in the substrate temperature range 830-1030 K. Films obtained from thermal beams (0.079 eV) grow only through the facile mechanism involving the reaction of out-diffused silicon atoms with precursor species, identical to the growth of so-called "buffer layers" via the reactive conversion of the silicon surface. At moderately higher kinetic energies (0.45 eV), a second growth mechanism opens which operates in addition to the silicon out-diffusion process. Growth at the higher incident energy can grow thicker films, i.e., is not thickness-limited, and occurs with essentially the same rates with or without a buffer layer. The morphological evolution of films grown on bare substrates proceeds through a pitted buffer or transitional layer, which allows,for the relaxation of strain due to lattice mismatch. The continuous, void-free films eventually obtained exhibit the doubly degenerate domain structure characteristic of cubic epitaxial material growing nearly two-dimensionally. Furthermore, remarkable square-pyramidally shaped and azimuthally aligned isolated three-dimensional features identified as Si islands are observed to grow simultaneously with the two-dimensional SiC film. Films grown below 900 K, though also epitaxial beta-SiC, do not show these isolated three-dimensional features, and are much rougher than films grown above 900 K. These results emphasize that new, enhanced growth regimes for electronic materials deposition can be achieved by using high-intensity and velocity-tuned supersonic molecular beams to deliver kinetically accelerated neutral molecules for use as efficient growth precursors. These experiments also suggest that lower substrate thermal ranges may, for favorable cases, become accessible for growing high-quality films when using supersonic molecular beam epitaxy (SMBE) deposition methods.