I did some mileage upgrades around the time of the merger, but since then I've been selecting SWUs as choice benefits and confirming the ungrades at the time of booking as the cost of upgrades with miles would have been far more than the miles offered as PM or DM choice benefits. All of my SWU upgrades should have worked equally well with miles in that they were confirmed in advance.

In fact, going forward with GUCs, there's going to be the decision of whether to try a GUC or miles whenever I need to purchase an expensive international coach ticket.