The A8 5500 is somewhat weaker than the Pentium G3258, and that GPU is comparatively low end. The should work well together.
I'd lok at turning off some of the effects in the .ini file (like motion blur) to stt if that helps.
C:\Program Files (x86)\Steam\SteamApps\common\Viscera Cleanup Detail Santa's Rampage\UDKGame\Config\UDKSystemSettings.ini