UPDATE:
Apple Customer Relations phoned me back as promised and the lovely Irish lady at the UK/Ireland head office has been in touch with one of the senior technicians, as I had the day before, and they are doing a 'force replacement' for me. Another returns box is arriving on Monday and I have to send the defective iPad back again, as soon as they receive it they are sending me a replacement. This is called a 'force replacement' where the repair/replacement guys are contacted, notes left, etc. and they just swap it out, no questions asked.
I can't praise the 2 guys at AppleCare Customer Relations who have/are handling my case high enough. They have gone out of their way to sort this for me and everything they have said, they have followed through with. They have reassured me that if the replacement has they same (or any other) problems, to simply call them back and they will sort it again for me. Her actual words were, 'I will work with you on this case until you get the outcome you want and are happy with'. This is very reassuring.
The replacement will not be a refurbished model, however, it will come in 'simple, plain packaging' but these are brand new models just set aside for replacements. The senior tech guy has reassured me of this and said there will not be any iPad 3 refurbished models yet as it's still to early on for this.
I asked if I could have one selected with a DY serial number but he didn't think this was possible as there are so many of them it would be very hard for the guys doing the replacements to riffle through all the iPad's looking for specific serials. He said, they come over from China on huge crates and one is selected and then sent out. This is understandable.
He then reiterated that if the new one has any problems to get back in touch and they would sort it for me. He also said, there will be good and bad in all batches/serial numbers and I suppose this is true as I have seen good screens from people who bought on launch day.
DY serials are the new batches by the way, this was confirmed to me.
So I will have iPad #4 Tuesday/Wednesday. I will follow up once I receive it. Here's hoping this one will be The One lol.