Re: 2560x1440 not working..
It's strange that it's 16xx... It should be ~1920x1080. Try to use your adapter in macos or google for some successful experience with any non-apple addapters.
OS: Gentoo Linux, ~amd64. VideoCard: GeForce GTX 470. ASUS P8P67 Deluxe, 2x4GB DDR3-1600 CL9, Core i7 2600k.