Ok, I think that Linux Mint 13 works pretty well for dual screen setups if you want to downgrade a bit. Ubuntu 12.04 LTS works ok too, but from what I've found, Mint 13 is superior. Note that Mint 14 doesn't work as well. Make certain you get Linux Mint 13 "Maya", not 14 Nadia. I'm new to Linux, so I'm not 100% sure.

Still, try LM 13. See if it works...