First of all , if u doesn't have decent pc , or u feeling uncomfortable when playing , or even u have laggs , first step is refuse trucolor (texture quality/size in setup.exe) , set compressed textures.
Second step as everyone know is refusing of antialising , its very hard performance killer
Third step is alternative d3d9 wrapper called d3d8to9 by crosire , it has bit better performance instead of dgvoodoo (CARE: not all pc supports this wrapper)
Fourth step is obviously refusing of hard performance killer mods : Real car facing and Reshade
Fifth step is tweaks for draw distances of world and cars , first one u can optimize in Mafia\scripts\Mafia_widescreen_fix.ini parameter "New Distance " (also u can simply change draw distance in graphics menu ). Second one in Mafia\scripts\Patcher.cfg , it has two performance killer parameters : PatchTrafficLimit , set it to 0 to not allow game use more than 100 cars in traffic density ,second one is TrafficSpawnDistance , set it to ~200-250
Ok ,here is easy tips for tweak performance , hope u did it correct and enjoying game right now <3