The resolutions that are selectable on your computer are dependent on both the computer configuration, and resolutions supported by the monitor or display. In this case you could try creating a custom resolution, but according to the processor specifications it is likely that you will no be able to achieve this resolution.
My monitor does support 2560x1440 resolution - it is a 2560x1440 monitor so to speak (27").
My question was not whether a laptop with an i7-6500u processor can run with a monitor at 2560x1440 resolution, because I know it can according to Intel's own specifications: Intel® Core™ i7-6500U Processor (4M Cache, up to 3.10 GHz) Specifications
My question is regarding the Hz. If connecting via DisplayPort, 60Hz would be no problem. But how about HDMI? Intel's specs states that it would run via HDMI at 24Hz at an 4096x2304 resolution, but would it be able to run with higher Hz if the resolution is lowered down to 2560x1440?
Note that support of the resolution in question on an external monitor is not just a matter of the CPU and its built-in graphics chip (many laptop models with that combo support 2560x1440 (WQHD) on their built-in screen), but also of the motherboard it's running on, specifically its HDMI port.
So if you want to be on the safe side when doing that purchase, you should choose a laptop model whose specification explicitly states that externally connected WQHD monitors are supported with their full resolution.