OK, I think I discovered what's causing the slowdowns. If HI-RES mod is turned on and your graphic card is 2D or integrated Intel crap, then it will run like a PowerPoint slideshow. Forcing the game to use the 3D card makes it run smooth!
If I can play on Intel crap (HD 4600 mobile) ATOM RPG/Trudograd without issue, then how "ancient" Fallout 2 engine together with Hi-Res patch could be so demanding in FY?