I recently had to look at some high-end tape drives.
LTO-Ultrium 3 seems to be about the fastest readily available - up to 80MB/sec native - and capacity (uncompressed) of 400GB per cartridge.
DLT seems pedestrian in comparison!
I am actually very fond of the DAT / DDS drives, because of the very small format. Capacities aren't too shabby either.
SD