The Dell U2723QE monitor has excellent accuracy before calibration in the sRGB mode. However, the white balance is a bit off, particularly with brighter shades of gray, and the color temperature is colder than the 6500K target, giving the image a blue tint.

Unfortunately, using the 'sRGB' Color Space setting locks the 'Red', 'Green', and 'Blue' settings in Custom Color. So, if you want to use those settings, you need to change Color Space to something else, which results in oversaturated colors and worse color temperature, as you can see here.