I was going to give up; but a further attempt remained: to try the conversion DVI (monitor) to HDMI (notebook).
Truly, this allowed me to (Selected the Display) set again the 2560x1400 32bit 30p Hz CVT through the INTEL function above (last update here: http://downloadmirror.intel.com/23885/a08/win64_153322.zip)
Note that this setting was apparently rejected, but after closing and opening again (mouse right-click on the desktop) this new option was visible in the Custom Resolution list.
So far, going to the Display Properties I could see not only, near the 1920x1080, the 2560x1400 for the Dell "U2713HM (Digital)", but even this time it was set as (Recommended).
Bingo!
Don't warry if on your click to Apply, the sistem hangs again. Be patient, on restart it should be all right, perfectly working (or at least still adjustable): to me, no icon displaced now and the hibernation is immediate and fully functional.
If you use Virtualbox, don't forget to run-update the Extension_Pack thereafter.
Good luck. ;)