Hi,
there are so many different things that affect the "payload" speed of any network-connection to say nothing about Wireless ones that I'll send you to a few links:
The 1st one gives very good technical info on why 54 Mbps is not possible:
Wireless Networking Speed: Ideals and Experiences
The otherone is a PcWorld testarticle using the newest technologies: they achieved max apr. 15 Mbps!
Unwired for Speed - What the Numbers Mean: Wireless Speed Trials - Review by PC Magazine
HTH
Petri