I profiled my XL20 in Custom (until it was retired) with the exact same equipment. I would typically use the color mode control to get close to 6500K. I think I usually used "warm1". This works on the XL series but not on regular monitors. On the XL, the color mode adjusts the RGB LED backlight rather than the LCD panel, so it doesn't promote level clipping. From there, I could either let match do the fine tuning with the video card or do a small correction with the RGB gain controls. Make sure that you don't set any of the gains above 50. Make subtractive corrections to the other 2 channels rather than raising any of them above 50, if necessary.