Hi Tkirk29,
Dell has tested this system with following video cards :
- AMD Radeon HD 7870
- AMD Radeon HD 7770
- AMD Radeon HD 7570
- NVIDIA GeForce GTX 660
- NVIDIA GeForce 640GT
- NVIDIA GeForce GT620
As, you mentioned that you would be using the system for gaming, I would suggest you to go for either GTX 660 or Radeon 7870 as GT640 might not be able to handle these games effectively.
This recommendation is based on my personal experience. I have used these cards myself and have been able to play these games at High settings and good framerates.
You may refer to GTX 660 review Here.
You may also refer to XPS 8500 specification Here.
Hope this helps.
