What speed do you get from
download.com's speed test Drifter? I use encryption on my home network and get a
steady 1360 Kb/s nearly every time. What are your results?
Remember that WM5 is always going to be slower than 2003 because of its method of using ROM and RAM with an emphasis on not losing data rather than the emphasis on speed in 2003. Were you using 2003 on the X50?
Some tweaks are available to speed up WM5 in general.
Did you install the driver rollup package available from Dell? Some slight wifi improvements were included with it, but I think they were only applicable to traversing multiple access points.