The seat map is moot, what matters is that it's already BOOKED 8/8. Someone just hasn't been assigned that last seat. The option to upgrade with miles expires at T-24 so you won't be able to see your position on the list before you have to make the decision. Seeing as it will come down to the T-24 list, I personally wouldn't bother with miles since you will be VERY high on the list, if not #1. That being said, if you REALLY want to get any potential seat that opens up then use the miles.