I've had no issues getting a perfect picture with my Apple USB-C HDMI AV adapter connected to a Dell 2515H monitor at 2560x1440, however have tried the same with a HP zr2740w monitor, with an HDMI lead connected to DVI and the picture is covered in red, green, and blue speckles even though the resolution is achieved. The picture is usable but certainly imperfect, and doesn't change in quality even at lower screen resolutions. I have tried other HDMI to DVI cables (including quality DVI-D cable), and the result is the same. I tried an HDMI to Displayport cable, but no signal was received by the monitor and this resulted in a black screen. I have also tried different refresh rates through QuickResX but still no difference. The latest 10.10.4 version of OS X claimed to fix some monitor issues, but has't changed a thing. It looks like I'll have to wait until a proper USB-C displayport adapter (i.e. one that allows charging) arrives, or are there any other solutions worth trying?