I am on the 6th iMac, after waiting a month or so I decided it was time to try again. The iMac is perfect except for a slight yellow tinge in the middle of the screen towards the bottom, and a bit on the bottom right corner. It is a week 53 i5.
As I got 10% off, I am thinking I will just keep this one and also request a screen replacement later on down the track once Apple figure out what is wrong. Hopefully by some miracle it might just be sorted with a firmware / software update.