"As long as that SSD doesn't stall trying to pull blocks off the top of that queue, it really doesn't matter how deep it is. So if you have 10GB of free space on your partition, you only need to call wiper.sh / fstrim once every 10GB worth of file deletions."
This isn't necessarily true. Earlier Trim will improve the performance of the SSD drive because the drive knows more free space -- more free space allows the drive to 1) pre-emptively erase flash 2) coalesce fragmented blocks 3) more efficiently combine write blocks 4) perform wear levelling operations with less overhead.
Early trimming can have a similar effect to the manufacturer increasing slack space which increases performances on nearly all SSD's.