I do recommend the move to LTO5. However a point to consider is that the LTO5 drive cannot read the LTO1 tapes, so the data will either have to be migrated to LTO5 or keep a LTO1 around.
Initially I would keep the backup configuration the same, just simply swap to LTO5. Then run test jobs directly to tape as well as test restores.
How often and quickly restores are needed is a big factor in deciding to go direct to tape or not. If tape is kept in house it might not be much of a difference but if tape is sent off site that would be a big factor in keeping backup to disk. After you have the data from the tests then you are in a better position to decide to go directly to tape or not.