Why does Warhammer III stutter during massive magic battles?

I felt total despair during massive magic bombardments; the screen stuttered so badly it killed the immersion. I tried enabling Extreme Performance mode in the BIOS, but while frequency stayed at 6400MHz per BIOS, my CPU hit 95℃ per HWiNFO, making my fans roar without fixing the lag. I then used the GamePP Resource Scheduler to elevate the game process priority from Normal to Realtime. This worked perfectly. Frame time dropped from 68ms to 14-21ms per RTSS, and memory bandwidth hit 72-89% per AIDA64, while temps stayed at 54-60℃.