Ultra-hard composite constructions comprise an ultra-hard body having a plurality of diamond crystals bonded to one another by a carbide reaction product. A reactant material is selected from materials that are strong carbide formers to form a carbide reaction product with diamond at HPHT conditions. The body includes a high-density diamond region positioned along a surface portion of the body and that is substantially exclusively diamond, and that has a diamond volume content of 95 to 99 percent or more. The high-density diamond region can form a working surface of the composite construction. A substrate can be attached to the body, thereby forming a compact, and can include metallic materials, ceramic materials, carbides, nitrides, cermets, and mixtures thereof. An intermediate layer can be interposed between the body and the substrate depending on the substrate and/or method of attaching the same.