Terminator T-800 GTA IV on old Pentium Dual-Core E5400 + NVIDIA GTX 460 video card

Game: Grand Theft Auto IV mods used: Arnold Schwarzeneger T-800 made by wapeddell & i also use a native mod for the god mode. As you could see, rain weather and night time will not help my FPS, i should record with sunny days, but sunny days will not fit with Terminator, lol. Rig spec: Old Pentium Dual-Core E5400 2,70GHz + 4GB RAM Video card: NVidia GTX460 or GTX 460 with 1GB DDR5 memory FPS: 7-15 ( recording with FRAPS ) + ( medium-low settings ) FPS: 13-18 ( recording with FRAPS on sunny days and no rain weather ) FPS: 18-35 ( when no recording ) + ( Medium-high settings )