This is a tweak I found and use to get 2560x1440 resolutions on my 3 benq gw2450 24" monitors that have a native 1920x1080 resolution. I have no noticeable hit to system performance with this either when gaming on a single one of the monitors. Certain games I take a fps hit when playing in surround mode @ 7680x1440. Your experience may vary depending on your setup.

open NVidia control panel / change resolution / select customize at bottom / in new window click create custom resolution / enter your selected resolution in the boxes provided, in this case 2560 horizontal and 1440 vertical / Then click test. Your screen will flash and you will be asked to save custom resolution if it worked or told it failed.
Simply save the custom resolution and when you go back to change resolution in NVidia control panel your new resolution will show in the list under "custom", select the resolution and click apply. Of course some monitors will go higher than the resolution my monitors will with this trick. Just enter the resolution you want to try on your monitor and test.

Hope someone finds this helpful if like me you would like higher resolution monitors but just cant afford them.

Enjoy