Tom,
We have just upgraded from V2.7 to V3.2.0.6 in the weekend (I guess your
3.4.0.6 is a typo).
Our HW is similar with Gbit (one), AIX 4.3.3 and ESS. We am not using the
new option SORT_FILE. I tested with different MULTIPLEXING and ended with 5
as the best value for performance (probably depends on the layout of the
filesystem in the ESS). 2 streams.

2 x 3590 E Tape drives (probably faster then yours but we only use 2), TSM
4.1 server, 4.2.1 client and rl_compression ~1.4

BKI1215I: Average transmission rate was 210.716 GB/h (59.937 MB/sec).
BKI0020I: End of backint program at: Tue Jan 22 02:10:11 2002 .
BKI0021I: Elapsed time: 01 h 50 min 51 sec .
BKI0024I: Return code is: 0.

Or old backups was slower but we have also moved to new HW and ESS in
connection with the upgrade which all improved the performance. A backup
test with the old SW and the new HW gave use ~2.5 hours but that also
depends on which tape drive it hits (2 are Ultra SCSI attached, 1 is FW
SCSI).
Regards,
Jan Norback
Tivoli Certified Consultant: ADSM/TSM
IBM Cert. Adv. Technical Expert RS/6000 AIX
Atos Origin-IT (MS/DS/OSS Unix)
VA-106, PO-box 218, 5600 MD Eindhoven, The Netherlands
Groenewoudseweg 1 5621 BA Eindhoven, The Netherlands
Email: Jan.Norback AT Atosorigin DOT com
Tel: +31 (0)40-2780289
Mobile: +31 (0)6-12994492
Fax     : +31 40 2783962