As a side note I was amazed on my last famil flight which was on an A388 from Auckland to Brisbane. Cruising at FL4XX at what was probably M.84 or so and 260 odd indicated or whatever it was and were assigned a delay of 15 minutes. I was very impressed at how slow the A388 can actually fly, we slowed down to about 210kts IAS and started a gradual descent for next 100nm or so. Still needed a lap of the pattern but it surprised me how flexible that aircraft is.
1Charlie, that is the crux of our beef! We can do amazing things with sufficient notice. The 250nm brick wall isn't really sufficient time for large losses.
On my machine fuel burn (including
5% allowance for racetrack hold) burn at altitude vs holding at 1500'
10,000' -4%
FL200 -7%
FL300 -7%
FL350 -6%
There isn't any benefit staying high to hold. By holding in a straight line you save 5% right off the bat. In general I find I only burn half the holding fuel by descending to say FL250 vs continuing at flight planned cruise altitude then entering the pattern to lose the same time. Slowing down at optimum altitude doesn't lose much time, due to relatively high minimum speed. Each aircraft will have its own profile, twins need to consider engine failure at min speed at high altitude, not so critical for an A380.
PER seem to have a good system, you blast off heading south, pass an estimate for JULUM, ATC get back with a crossing time and you use the next hour or two to lose the time, 15, 20 or even 30 minutes is possible with sufficient notice.