Adding extra lanes to the highway, without increasing the speed limit does not make the cars go any faster. Perhaps a poor analogy but non the less true.
In the case of the router, your wireless cards would need to upgraded to G in order to get those 54mbs speeds from the router. However if your internet is chugging along at 1.5mbs, going from B(11mbs) to G(54mbs) shows no increase. The only positive is in LAN transfers, files will move faster.
Basically the same logic for CAT5 to CAT6.
I heard that upgrading wireless router from B to G does not really improve internet speed for your wireless. How about upgrading cat5 cables to cat6?

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