I'm running an Exabyte Mammoth. 20gig tapes. They claim 3MB/sec (uncompressed) 6MB/sec (w/hardware compression in drive). I get 2 - 2.5MB/sec. w/video files.
Had a lot of problems at first. They shipped a bad tape with it. Then I found out it needed active termination, not passive. It backed up reliably after this but sometimes had problems restoring. This even after doing a full confidence backup (reading back every write operation as you go) w/no errors. Finally, after many months, they came clean and said they were having a driver problem w/NT. Downloading their new one a number of months ago ceased all problems and it has been bulletproof since.
BTW, the Exatape brand tapes Exabyte sells are actually OEMed by Sony. Somewhere I have the equivalent Sony product no. for the Exabyte 170e AME 20 gig tapes, but no supplier has been able to procure any from Sony yet to my knowledge. I have heard that the tapes are scarce even from Exabyte, though I haven't tried to order any myself recently.