> The group I work with is expecting 160-200MB/s megabytes
> per second on an LTO3 with compression. [...]
> 
> So nobody gets 160-200MB/s even with 2:1 compression?

You missed the previous poster's (Wilts) point:  you haven't isolated
tape speed from the process of getting data to it.  Read the tuning
manual as suggested.

Whether your test data are random or they are all zeros, it still takes
exactly the same amount of time to get them from the disk to the tape
drive; tape-drive compression will have no effect until data delivery to
the tape drive is faster than the drive's native throughput.