But I still don't get it. A single engine failure is totally different from an all engine failure. Considering windmill starting and x-bleed starting + geographical location makes it NOT a one horse for all courses scenario. Hence I'm puzzled. The high speed for all engines failed came to the fore after BA B747 lost all engines in volcano ash over Indonesia. The scenario was unknown in detail, and it was suggested in the aftermath that the high speed descent prevented the engines from seizing up in cooling silicon ash.
A single engine failure and drift down profile followed by either a x-bleed start or then an increased IAS for windmill start is for crew planning. Cruising at 250kts/M0.8 then single engine failure at FL>300 and increasing to 280/300kts when possible just doesn't seem the way to go.
I must be missing something.