Pick one and press Start, then click Next › to step through it.
The LSM's load staying low while writes dominate, and the B-tree overtaking it once reads outnumber writes by about half again.
That the fork is a trade of amplifications: a B-tree pays on writes (random in-place updates), an LSM pays on reads (checking several levels).
Weight each side's reads and writes by its amplification, compare the disk loads, then drag the write rate to find where the winner flips.