Prior to installing patch DLT7000 tape drive was running at 5-6 MB/s and tape
capacity is 70GB.

After installing patch performance drops to 1-3 MB/s and capacity drops to 40GB.

Amending st.conf to use the following values has no effect.
tape-config-list=
        "QUANTUM DLT7000",      "Quantum DLT7000", "DLT7k-data";
DLT7k-data =    1,0x38,0,0x1D639,4,0x82,0x83,0x84,0x85,2;

Backing out patch appears to fix problem.

Despite appearances this is not an error. Here's why......

Solaris 2.6 with patch 105847-01 had no built-in support for DLT7000 devices 
due to bug 4135251.

DLT7000 tape drives were detected as Generic SCSI Tape device.
This means that whatever density modifier (l/m/h/c/u) is used on the /dev/rmt 
device name the st driver will always send a density code of 0x0, effectively 
telling the tape device not to change density from it's power up default density
of 70GB compressed mode. 

Once patch 105847-09 has been installed the st driver fully supports the DLT7000
device and will send the correct density code depending on the modifier used 
(see table below). Therefore if a density modifier of m is used, the st driver 
will send a density code of 0x83 which will tell the device to run in 40GB 
compressed mode, which happens to be DLT4000 emulation. Hence the poor 
performance and lower capacity.

,------------------------------------------------------------¬
| Tape    ||   l  |   m  |   h  |  c/u || Density modifier   |
| Device  ||  Off |  On  |  Off |  On  || Compression on/off |
|---------||------|------|------|------||--------------------|
| DLT4000 || 0x80 | 0x81 | 0x82 | 0x83 || Density code       |
|         || 10GB | 20GB | 20GB | 40GB || Capacity           |
|---------||------|------|------|------||--------------------|
| DLT7000 || 0x82 | 0x83 | 0x84 | 0x85 || Density code       |
|         || 20GB | 40GB | 35GB | 70GB || Capacity           |
|---------||------|------|------|------||--------------------|
| DLT8000 || 0x84 | 0x85 | 0x88 | 0x89 || Density code       |
|         || 35GB | 70GB | 40GB | 80GB || Capacity           |
`------------------------------------------------------------'

The solution to this problem is;
Leave patch 105847-09 installed, do NOT modify st.conf. Change the device name
used to write to the device. Use h for uncompressed 35GB or c or u for 70GB 
compressed.