Strange, the ath5k driver has done great step forward in the last few month, and now it works generally very good.
What you mean with slow? Keep in mind that the connection bitrate is adaptive, it jumps from 1Mbit to 54Mbit as soon as it's needed.
Anyway, if you are sure the current driver is working slow, try to install the 'linux-backports-modules-karmic' package, containing a newer ath5k driver that may fix your problem.
Instead, if you plan to continue to use ndiswrapper, set the following options in '/etc/default/samsung-scripts' in order to make the scripts work good:
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