I wonder if, even with gear down & speed brake, you could reduce speed to anywhere near F5 limiting speed. Indeed I'm curious if lowering the gear at 270kts, with 1 donk at 100% will slow it down. I expect that overhead at a good height and dead stick it would be a safer bet. At least you know what is going to happen when you dangle all the bits that will help. The last thing you want is bits flying off and causing unexpected severe handling problems low down.