I did have one little problem though.
I have a DLT tape drive, on an Adaptec 29160N SCSI controller.
The backup speed fell dramatically, by about 5x.
It turned out that while the 2405 used an Adaptec driver, the 29160N used a Micro$oft driver... evidently winXP comes with a driver for the 29160N. Replacing the M$ driver with an Adaptec one (all the way back from 2004) fixed this.