How do I fix high I/O wait causing lag in Splinter Cell on Intel 660P?

During stealth in the factory, the lag felt like a personal attack. I tried cleaning temp files, but the stutter persisted. I used GamePP to set the process priority to Real-time. AIDA64 showed disk temp stable at 48-55℃, and frame time dropped from 14.3-18.1ms to 9.1-10.4ms. The game finally saved my immersion.