That's the problem we are experiencing at the office right now. We have been archiving to tape for quite sometime when we were starting with LTO3. Now we are at LTO5 (always one generation behind so the cost will be cheaper.)
The problem is backup speed. Our data are incompressible data (video, pictures) so we do not gain from the very high published backup rates. Our arrays are high speed hundreds of megabytes for streaming uncompressed video (even this is not compressible by the tape, which is very odd.) With terabytes of data generated, it is hard to keep up with backup. Our data is regularly restored because of access to archival storage. This creates data management challenges as well. Our main problem is the very long time to backup and restore TBs worth of data on a daily basis. Though it would be easier to scale by adding more tape libraries, but it is not cost effective to keep on adding (as well as adding more arrays to handle streaming read and write operations at the same time.) We are also using LTFS which automated backup software are not friendly too. Our requirement is different from the enterprise backup of multiplexing data from different servers at the same time to get speed. We backup projects one at a time on a tape (self contained.)
LTO6 does not go faster much from LTO5 speeds (160MB vs 120MB for uncompressed.) It is likely that the tape is reaching its limit (much like harddrive speeds have not grown with capacity increases over the years.) SSDs are faster but not effective in capacity wise though. So time to look for new technologies in storing and accessing data. In all, storage has not kept up with the performance improvements in CPU, memory, and other bandwidth links (Ethernet, fibre channel, etc.) We should be transferring at the 10GB/s range already at this time.