Dental impression materials are fundamental to the production of accurate dental prostheses and restorations. This study focused on the formulation and characterization of a novel, plasticizer-free condensation silicone paste, comparing its performance to a commercial benchmark, Speedex. A specific laboratory paste was developed using 39 vol% hydroxy-terminated polydimethylsiloxanes (PDMS-OH), a high concentration of inorganic fillers (60 vol% silica and calcite), and 1 vol% tetraethyl orthosilicate (TEOS). In contrast, characterization of Speedex revealed a lower inorganic filler content of approximately 40 wt% and the likely presence of plasticizers. A detailed comparative analysis of physicochemical, rheological, and mechanical properties was conducted. The high-filler laboratory formulation demonstrated significantly improved dimensional stability, exhibiting less shrinkage over 12 hours compared to Speedex. This enhancement, however, resulted in a predictable trade-off in mechanical properties. The formulated paste was substantially stiffer, with a higher elastic modulus (4.8 ± 0.2 MPa vs. 3.63 ± 0.12 MPa) and a slightly greater Shore A hardness (62 vs. 60), but it showed markedly reduced ductility, with a lower elongation at break (36.69% vs. 51.82%) than the more flexible commercial material. Rheological profiles also differed notably, reflecting their distinct compositions. These findings highlight that a high-filler, plasticizer-free formulation strategy can significantly improve dimensional accuracy, albeit at the cost of reduced flexibility, providing valuable insights into the structure–property relationships that govern the performance of condensation silicone impression materials.