The lag spikes and a missing ceiling

[plutomaniac]

6GB of RAM is more than enough. From personal experience I can tell you that the problem is the slow hard drive. When the game got out I tested it on an old SATA I (5400RPM) hard drive and the game was lagging whenever I dropped an object or moving fast, basically upon loading of a new file. I moved the installation into another proper drive (faster HDD or SSD) and these issues disappeared completely. You should also update your AMD drivers to the latest possible for good measure though.