DLT Read Throughput - SDLT160/320

[Pat_96]

Have a HP MSL5026 Library and am restoring DLTIV media.
Just wondering if anyone has had better throughput speeds when restoring DLT IV media on an SDLT one drive - Catalog time is just a few minutes, but go to restore and its about 10GB per hour i.e. one tape will take 3.5 hours to restore.
(178MB /min actual as apposed to 15MB/s listed performance).

Even on my old [not working] TZ891 in ESL9000 Library circa 1999, I was getting 20GB per hour restore.

Is it simply that reading DLT media is just going to be slow on SDLT drives ? ?
Cheers