I've had a T-Mobile Sony-Ericsson card, and was overall pleased with it -- there
were a few occasional glitches with the Wireless Manager software, but they may
have been the OS's fault. Caution: it died when I tried to use it on a desktop
in a PCMCIA slot provided by an add-on card; it turns out the SonyEricsson requires
a nonstandard 3Volts on one of the pins and the slot misread it an gave it 5Volts
Ever since I got a Blackberry, though, I have been using it as a tethered modem and
thus have no need for an extra card. (Not to mention that PCMCIA slots have started disappearing from laptops!)
Speed is about the same -- if anything, the BB-as-modem is faster. I would suggest that you try it!