I think X3800 is about right for your rig. Your score would be slightly higher if your CPU were better. In a game like Skyrim, which is very dependent on CPU power, your CPU is holding you back. IMO it's not a great idea to be running two cards on that CPU - it's probably bottlenecking your 7870s.
To show you how crazy demanding the Extreme preset is, here's 7970 Crossfire overclocked to 1225/1800 and a 4.8 GHz i7-2600k:http://www.3dmark.com/3dm11/3761057