We will be doing r/t LAX to Sydney on a Delta 777. We have enough miles to cover the fare in coach but not enough for comfort. If I use miles plus cash for the same number of miles plus an additional $300 each we can get the extra 4" legroom. For two 14-15 hour flights it seems like it may be worthwhile (I am 6' - she is 5'3"). But maybe at 6' I can handle the coach legroom? The longest nonstop flight I have taken was Seattle to Dallas so this is a big difference. Any thoughts?