The first tapetype below I measured today (with a 150m tape)on a new
DELL PowerVault 100T DDS4 tapedrive (Archive Python 06408-XXX)
with hardware compression turned off (dip switch 1->OFF).
Maybe it will come in handy for someone else..
Note I lowered the capacity to have some buffer. Edit at your
own preference..

define tapetype PV-100T-DDS4-150M {
   comment "produced by tapetype on adelphi , no hw compression"
   # measured: length 19457 mbytes
   # leave some for tolerances...
   length 19000 mbytes
   filemark 32 kbytes
   speed 2686 kps
}

This one I found somewhere on the net:
I would be interested in possible reasons for the
3GB difference in capacity (and the marked diff in
filemark sizes!).
The speed may be due to SCSI configuration
(other controller, more devices on the same bus etc)

define tapetype PV-100T-DDS4 {

       length 16534 mbytes
       filemark 0 kbytes
       speed 2278 kps
}

regards