I don't usually post but I wanted to chime in here. I have a Sony Viao 2.4 GH -I have a 128 mb graphic card-1 gig of ram-80 GB HD- It is 6 ys old.
I have had no problems with the game (knock on wood). It loads fast, I have the graphics set on high, I can play for 8 hours or longer at a time and no slow down. Even large houses are no problem. I have to say I am surprised myself. I have had children..and did just about everything that I  would expect would slow me down.
Does anyone know why that would be? I keep thinking maybe there are other issues with some peoples
games/settings on the P.C. that might be causing problems. Just a thought.