Far Cry 2

Far Cry 2 utilises it's own engine called the Dunia Engine. Developed by Ubisoft specifically for this title which is a sequel to Crytek's developed Far Cry which utilised the CryEngine. Some of the technology utilised in the Dunia Engine is:

• Destructible Environments [EDIT] Not true, environment is static and can't even be scratched.
• Dynamic Weather
• Dynamic fire propagation (influenced by weather system)
• Dynamic vegetation (RealTree), including growth and regrowth of vegetation [EDIT] Not true, vegetation is static, and spawns back after a period of time when destroyed.
• Full day/night cycles
• Dynamic music system
• Support for large player maps, without specific levels
• Non-scripted AI
• Radiosity, or non-direct lighting
• amBX technology from Philips for special effects, with the proper hardware
  

This engine also supports DX 10 under Vista, and DX9 if the user is running XP. The engine is quite similar to CryTek's CryEngine 2 used on Crysis and Crysis Warhead.

NB. List taken from Wikipedia

Settings

Very High: 1600 x 1200, 8x AA, all settings "Ultra High "DX10 enabled in Vista, not in XP.
High: 1280 x 1024, 8x AA, all settings "Ultra High "DX10 enabled in Vista, not in XP.
Medium: 1280 x 1024, no AA, all settings "Ultra High", DX10 enabled in Vista, not in XP.
Low: 1280 x 1024, no AA, all settings "Low."

In Far Cry 2, the 4850 holds it's own very well, in fact beating out both the 9800 and 4870 x2 under Vista at low settings and keeps almost level with the 9800 at all others.