This has been tested and shown to work.
Boring story about Amazon's slightly screwy shipping system...
So, I pre-ordered some stuff on Amazon. I ordered it with FREE Super Saver Shipping, grouped into as few packages as possible. I looked at the delivery date: next month, even though everything is published within the next week.
So I switched it over to standard shipping, and it predicted that my delivery date was a full week earlier. Which was, well, acceptable, but not great. Price: +$5.
So I switched to delivering my order in as many packages as possible, as soon as things come in. The slow one is pushed up a week, the fast one is pushed up two weeks. Yay! Price: + another $3.
But, hey, let's change it back to shipping it in as few packages as possible... wait, "minimum shipment is two packages"? That's not any fewer. Is the charge the same? No, in fact, now we're back down $3, to simple standard shipping prices (maybe plus a dollar?). No change in the shipping dates...
Well, let's just see... we'll switch it back to "FREE" and... well, it's free again, but the shipment and arrival dates are still unchanged. A final three weeks earlier on one, two weeks earlier on the other.
But... but... all I did was go in a big circle!
There's a lesson in this... somewhere...