So the delay is all down to your proxy in the UK? I can't believe that, I would imagine with warning their delay would be same day or max 2 days.
Have you even read this sentence back to yourself? It is undecipherable.
What is more important is how long the actual delivery takes to a) get from 3 to your proxy and b) from your proxy to the states. As you claim to have done it, you should be able to say how long it took.
Again, this is all completely irrelevant. You make the decisions on when you wish the sim card to reach you abroad. You realise UPS / Fedex have different options available based on delivery times? Probably not.
My sim through standard international mail took no more than a week to reach me.