RISC-V-based Systems-on-Chip (SoCs) are witnessing a steady rise in adoption in both industry and academia. However, the limited support for Linux-capable Full System-level simulators hampers development of the RISC-V ecosystem. We address this by validating a full system-level simulator, gXR5 (gem5-eXtensions for RISC-V), against the SiFive HiFive Unleashed SoC, to ensure performance statistics are representative of actual hardware. This work also enriches existing methodologies to validate the gXR5 simulator against hardware by proposing a systematic component-level calibration approach. The simulator error for selected SPEC CPU2017 applications reduces from 44% to 24%, just by calibrating the CPU. We show that this systematic component-level calibration approach is accurate, fast (in terms of simulation time), and generic enough to drive future validation efforts.