Someone suggested this at GOG
Are you sure you turned off vertical sync ? Because that alone doubled my fps. Another way to further reduce slow downs apparently is to rename the ddraw.dll file in your fallout folder. I'm not entirely sure it works and it may affect your game in some other way (to be honest i have no idea what this file is for) but I tried it and so far it seems to be working. Now my game runs extremely smoothly. image