umm is this a serious question? they can descend at 210kts: if you remove the thrust then you've either got that or stall. most airlines look unfavourably on pilots who choose the latter
just as an example if you were 210kts then you'd generally need flap 5 to hold that speed doing 750'-800' per min on a standard 3 degree glide, obviously depending on weight and ambient conditions
but to be honest i don't really get your question. you'd definitely struggle to get any high rate of descent clean at 210kts