Optical detection using fiber-optic probes provides galvanic isolation, full immunity to electromagnetic interference (EMI), and the high sensitivity needed for early partial discharge (PD) detection in gas-insulated switchgear (GIS) and transformers. Silicon photomultipliers (SiPMs) are well-suited for on-site PD monitoring thanks to their compact size, single-photon sensitivity, and EMI immunity. This paper presents an application-driven evaluation of two silicon photomultiplier (SiPM) detector configurations, one employing an unpackaged SiPM with an external driver circuit and the other a fully integrated, packaged SiPM module using a physical-model PD simulator. We evaluate dark count rate, single-photon pulse amplitude, phase-resolved PD (PRPD) pattern, and voltage-dependent response. The integrated module delivers significantly lower dark count and clean EMI-immune signals but exhibits amplifier saturation at higher voltages, which limits its dynamic range. The unpackaged SiPM detector with lower amplifier gain maintains a positively correlated pulse response across the voltage sweep yet requires external shielding and shows denser self-noise. Our results show how microcell pitch, amplifier gain and package design affect sensitivity, noise level, and dynamic range. We provide practical guidelines for selecting or customizing SiPMs, balancing photon detection efficiency, recovery time, and data acquisition system complexity, to optimize on-site optical PD monitoring in high-voltage equipment.