I built this system specifically for gaming. The only parts reused from the previous system were the monitor, keyboard and moust, hard drives and DVD drive. The system can run most games at high settings, 60fps. The biggest bottleneck is currently the GPU, as it will come close to 100% usage in certain games. The CPU sits around 60% most of the time.
Skyrim - Ultra Graphics Settings - 1080p - 60fps Bioshock Infinite - Ultra Graphics Settings - 1080p - 20-30fps Diablo 3 - Highest Graphics Settings - 1080p - 60fps Dark Souls - Highest Graphics - 1080p - 30fps (limited by game)