Overall, thank you for a well-detailed review. I think another important point to mention is the warranty. The Alienware includes Dell's 3-year advanced replacement, meaning Dell will send you a replacement before receiving your broken screen. With so many comparisons to the Acer X38p, having a 2-year standard warranty, I think that Tom's should mention the support differential. Another important factor not evaluated is the noise. The AW3821DW is whisper quiet. The X38p has a noticeable fan noise that I can hear with headphones on if no sound is playing. The sound was driving me crazy.
I have owned the X38p (returned) and now I own the AW3821DW and can confirm the AW3821DW's HDR is mostly trash, but the color accuracy, screen size, g-sync, brightness, and responsiveness make it one of the best monitors I have used. I was able to purchase for around $1,300 in the US with a 10% off coupon and their sale. I would not be surprised if you saw the monitor get to $1000 in six months.