After two hours of Atomic Heart, my B360 Core ARGB temps spike and FPS drops, how do I fix this?

After two hours of gaming, this AIO basically turned into a space heater. The pump efficiency on the Cooler Master B360 Core ARGB seemed to decay by 10-15% under sustained load, meaning heat wasn't moving to the rad fast enough, causing a brutal clock drop. I tried undervolting in the BIOS, but my minimums crashed to 50 FPS—a total disaster. I used the official software to force the pump to 100% constant and set the rad fans to max out at 80℃. HWInfo showed the temp range shrink from a wild 60-90℃ to a tight 72-78℃, and the lag disappeared. The pump does make a noticeable humming sound at night now, but I managed to mask it by increasing the bottom case intake. CPU temps now sit at 75-81℃, and stress tests show a smooth thermal curve with coolant at 32-38℃.