Why does Final Fantasy XV stutter during large magic spells?

The effects are gorgeous, but the Bragi II DDR5 6800 failed me; every full-screen spell caused the game to stutter like a slideshow. I tried enabling 'Extreme Mode' in BIOS, but memory temperatures spiked to 65℃ per AIDA64, triggering throttling. I used the GamePP BIOS Load-Line Voltage Adjustment Wizard to lock memory voltage at 1.40V per CPU-Z and loosened tRAS by 10 cycles. RTSS showed frame time stabilized at 16-22ms, and AIDA64 confirmed temperatures dropped to 55-62℃.