I too had Screen problems on Custom conf. 27"
I have a 2 day old iMac 27" that I waited for 4 weeks for because I custom configured it. I discovered in the upper right corner near the apple logo of the screen its slightly dimmer then the rest of the display. Not sure if this is typical or not. Machine otherwise is fine, no dead pixels, geek bench score of 14433 and dont know if I should exchange or not. almost 3k is a lot of $.
I had problems with the Screen after a day, it looked like bubbles between the screen and the outside glass. You could rub them out but they would come back once in a while. also I have a 2Big Quadra USB 3.0 6T Raid external drive that drops out of the Finder when the computer goes to sleep. Also I was getting auto restarts on the computer.
My Configuration is:
27-inch iMac
Part Number: Z0MS
With the following configuration:
PROCESSOR 065-C0PK 3.4GHz Quad-Core Intel Core i7
MEMORY 065-0638 8GB 1600MHz DDR3 SDRAM-2X4GB
I installed 32GB of Crucial Memory.
HARD DRIVE 065-C0X7 768GB Flash Storage
GRAPHICS 065-C099 NVIDIAGeFrc GTX 680MX 2G GDDR5
MOUSE 065-0662 MAGIC MOUSE+MAGIC TRACKPAD
APPLE KEYBOARD 065-0664 Apple WL Kybd (English)+UG
COUNTRY KIT 065-0718 COUNTRY KIT
I have returned Two Imac and waiting for my 3rd. Like you said
In my case almost $4000.00 is a lot of money
I wonder if they are having trouble with the CUSTOM builds form that Plant in China. Are there others that are having the bubble problem or screen problem that are just living with them??