Maybe I am weird, but I refuse to buy backordered/pre-orders on material. I just don't need it that bad! It kind of annoys me to be at an online fabric shop to put material into my shopping cart only to find out it is not in stock because it is a preorder....
So in your situation, I would say NO to international backorders. It's not only about the postage, but also about the order tracking time. And like someone else mentioned, the timing and possible cancellations by the manufacturer/distributor.