I'm in a similar situation, except mine is about the storage.
I pre-ordered a 16GB iPhone 6 for in-store pickup which is now available for me to pick up tomorrow.
I've had 4 iPhones - 3 were 16GB and 1 was 32GB.
I don't really need the extra storage, but since I got married my wife and I have been travelling a bit more, which means I'm taking more pictures.
Shouldn't be an issue, worst case scenario is I stick with the 16GB and just have to manage my storage. Would be a dream though if they let me "return" and then buy a 64GB. Doubt they'll have stock though!