So I started another run of T3 after a break of nearly a decade and using the latest Sneaky Tweaker. But for the life of me I couldn't understand why the frame rate would crater into the 20's while panning around. I tried adjusting all the detail/shadow/light sliders up and down = no joy.

But disabling Anti-Aliasing has completely cured it. Sorry if this is old knowledge but it has transformed my playthrough - instead of grumbling about all the things they got wrong, I'm actually enjoying the things they got right. Never thought I'd say that.