It is shown that free-forging (upsetting with free lateral surface) and rigid die pressing modes provide different levels of densification under the same axial force applied during spark plasma sintering (SPS). Based on the developed constitutive model of SPS, an optimal combination of the above-mentioned pressing modes enabling the achievement of the highest final relative density is determined. A series of comparative experiments for a number of powder materials systems is carried out, and the results of the modeling are confirmed. The developed modeling-based concept of optimal SPS pressure mode is used as a basis for innovative SPS tooling design facilitating higher efficiency of consolidation. A hypothesis of the major impact of the inter-particle contact area evolution on the densification rate is put forward. It is argued that properly controlled interplay between surface diffusion and external pressure-imposed creep provides the better efficiency of the SPS process.