I think you'll find it's 80 MB/s ;)
You'll probably find that the tape drive isn't your bottleneck. The drive itself, with the right type of data will go that fast if the BE media server can supply it fast enough. I use an HP LTO2 drive, (up to 60 MB/s compressed, 30 MB/s uncompressed), and when backing up large files or Exchange information store, we can see over 3000 MB/min reported.