Hi,
For slow IrDA (SIR) the maximum connection speed is 115200 bits per second (or 115 kilobits per second). So you divide by 8 to get kilobytes per second (14 KB/s). Add in the fact that IrDA is half duplex - only one side transmits data at a time, lighting conditions and positioning of the devices can degrade the link quality, and also that the IrDA protcol has some overhead then, in practice, you probably only get about 7 KB/ s transferred. Getting 9.6K is quite good if you've achieved it!
Some devices (not the zaurus ) have Fast Infrared (FIR) which is 4Mbps which means it is in theory 35 times faster than SIR so you could get 245KB per second transferred.
Rob