The Thermalright Peerless Assassin 120 is the objective winner of this comparison, securing two out of three spec victories. Its most significant advantage is a 238% higher TDP rating compared to the Noctua NH-L9i-17xx, indicating a substantially greater capacity for thermal management. While the Noctua NH-L9i-17xx holds a lead in acoustic performance, offering an 8% better noise level, it cannot match the raw cooling potential provided by the Thermalright Peerless Assassin 120 across the evaluated metrics.

Users prioritizing maximum thermal headroom and cooling capacity should choose the Thermalright Peerless Assassin 120 for their system. Conversely, the Noctua NH-L9i-17xx is the superior choice for builders who specifically prioritize a quieter operating environment. By selecting based on these distinct advantages, users can align their cooling hardware with their primary system requirements, whether that involves managing higher thermal loads or maintaining the lowest possible noise output during operation.