Either I am reading this wrong or something is not right here.

Buffered:

windows = 0.006 linux = 0.03

80% Win for windows?

But where do those numbers come from?

The time in ms for linux was 522, the time for windows was 410. That's not an 80% win.

where does the "Write cost" number come from?

In general for the other numbers I don't think they are comparing the same things. I don't think it is a coincidence that the two systems had write times of both about 10s and 20s for the different tests. Where linux took 20s and windows took 10s I'd bet that they were comparing different behaviors.