This study examined the influence of silica type and loading on the mechanical properties of two bisphenol-A-based epoxy matrices, which are intended for application in fibre-reinforced composites. The investigation involved two commercial epoxy systems, LG206 and LG330, which were modified with fumed silica (Aerosil 200) and precipitated silica (Arsil) at concentrations of 1, 2, 3, and 5 wt.%. The materials were assessed based on density, tensile behaviour, three-point bending performance, unnotched Charpy impact strength, and fracture morphology. The primary selection criterion was the maximisation of Young’s modulus while ensuring elongation at break remained above 3%, as supported by flexural modulus and impact resistance data. The incorporation of silica generally enhanced the density and stiffness of the composites; however, this enhancement often resulted in decreased tensile strength, elongation at break, and impact resistance. Initially, LG206 exhibited greater stiffness and strength compared to LG330, but silica modification significantly reduced its deformability and increased brittleness. Conversely, LG330 demonstrated a more favourable response to fumed silica. The LG330 + Aerosil 200 systems-maintained elongation at break above the specified threshold while improving stiffness. The highest impact strength was recorded for LG330 + 2 wt.% Aerosil 200, achieving 21.67 kJ/m², whereas LG330 + 5 wt.% Aerosil 200 offered the greatest stiffness within the LG330 series while retaining acceptable deformability. Precipitated silica generally diminished impact resistance and induced more brittle behaviour. The findings indicate that silica-filled epoxy systems should not be optimised solely for stiffness; rather, a balance among filler type, matrix chemistry, and loading is essential to maintain deformability and fracture resistance.