Hi guys,
So I got the 16GB upgrade, apple really are taking the mickey with pricing (the difference between a 8GB and 16Gb kit of laptop ddr3 is about £42 here) so they're quadrupling their cost.
I looked at it this way, I want to keep this laptop for 5 years so if this upgrade extends the life of my mbp by just a year then it has paid for itself and it means I shouldn't run out of ram even if my workload changes or I feel like running a few more VM's.
I really appreciate your advice though and if the shipping date slips significantly on the custom build I would be far less hesitant to just cancel and go and pick up a 8GB model.