I have the same problem with the resolution.
Only i have 2 screens on win8.
Screen 1 : on HDMI - 1920x1080
Screen 2 : on DVI-D - Dell 2711 - max res 1680x1050 / 1600x1200
I tried to override the resolution using CustomModeApp.exe (with 2560, height 1440, 60 Hrtz, 32 bits, GTF) but i get the following responce
'The entered resolution expaned the maximum bandwith' (it's a translation from dutch, wont bore you with the original).