I cant tell you anything about the toshiba cards. I have a Panasonic 10 MB/s. Speed matters on the zaurus, since the 5500 uses jus one bit instead of four. With a 10MB/s you reach then 2,5MB/s. I am using the alternative modul from the download section here (under 5500er patches). It is faster as the original driver, but I dont if that uses all bits ( I think the bit thing is maybe a hardware issue).
I bought my panasonic for 74 Euros in Germany, but you uk people blocked the Euro. £65 sounds expensive.
Have fun,
Sam