For anyone who hasn't seen this other thread yet, it explains how to set custom resolutions on the latest Intel HD graphics hardware:
Custom Resolution on Intel HD 4600
Some users in another thread on Dell forums -- U3014; problems getting full performance through HDMI - Monitors Forum - Peripherals - Dell Community reported success via HDMI using a Dell U3014 @ 2560x1600, 16 bit, 60Hz, 2560x1600, 32 bit, 24Hz, 2560x1600, 32 bit, 36Hz, 2560x1600 32bit 48Hz, and even 2560x1600, 32 bit, 60Hz with CVT Reduced Blank (CVT-RB) timing. See the thread for details.