And ZFS is, by default, not meant for high burst speed of ridiculously big data stream. ZFS's defaults are to ensure fair I/O capacity for all tasks, and do extra integrity verification. If you want high burst speed with disk/etc I/O, you'd need to either use UFS with tuning that forsakes I/O fairness (and if you wanna go further, forsakes even system interactivity), or tune ZFS to do the same.
Tuning guide for ZFS is here: https://wiki.freebsd.org/ZFSTuningGuide
There are also many other utilities that can be used to prioritize a process for higher CPU and I/O capacity (which naturally means other processes get hosed, but hey, you don't care about that right?).
The reason why FreeBSD ensures interactivity over all others by default (by reserving CPU and I/O resources for interactive tasks) is because *BSD admins generally do not want their servers to livelock if some gung-ho process decides to go postal.
And you won't notice speed difference between FreeBSD and Linux if using normal apps that don't artificially spam-hog all resources.
Considering all the above, I think the benchmark is not representative of the true power a FreeBSD system can serve if configured properly.