@RossMacca just picking up on this, as I found myself in the same situation as you...
I assume your pre pre order was for Barclays monthly payments, right? Then you placed your Amazon order as a way of guaranteeing launch day (or at least launch day +1) delivery. What's your plan re your Apple order? As I say, I'm in the same boat, Barclays finance in place for the 3rd year running, Apple order delivery 3-10 Oct. Placed the Amazon order in haste, as I was gutted not to get the launch day delivery from Apple. However, now want the best of both worlds - the launch day delivery from Amazon, but the Barclays finance. Are you planning on returning your Amazon order before/when your Apple order arrives? Not sure what timescale Amazon orders can be returned in (or if even possible once opened/activated!)