Originally Posted by
YMCA
cyclingforums.com
go to the powermeter section
it will have all the nerdy advice you can handle
even from the mouth of the guys who wrote the books
or even up the ante on the nerdiness and go to the googlegroups wattage board.
kudude: the coggan/allen "racing and training with a powermeter" book has a chapter devoted to answering your question re: powermeters, albeit a bit dated, it's still applicable.
fwiw, cost -> benefit, the powertap wired version wins by a km, or at least several hundred dollars.