Update:
Went to the store ok, told the employee that I already had an existing online order - which we can cancel if all goes ok.
Apple employee made a little mistake when she was using her handheld - she accidentally hit cancel for the reservation. She was so nervous at this point and grabbed another employees iPad and luckily was able to reserve that phone again.
Did the usual activation/contracts etc. Yes the credit check was ran again and no issues.
New iPhone 7 plus activated, and I just did some basic setup for now.
In the store I then logged onto my account, and cancelled my existing order, the apple employee also called apple up to confirm that it was cancelled ok.
Will play with the new phone later - and this time I'm setting it up as a fresh one - not carrying over any backups for the 1st time. I'll let iCloud bring over contacts and some other things. Lots of apps etc to setup later.
So by looking with istocknow most days I've managed to get the phone two weeks earlier than my online order.
