Observations of one of our customers who sails the Carribean
The equipment on shore certainly makes a BIG difference in the range we can get (which certainly must have to do with the RX and TX ability of the access point). For instance, there is a pay internet service down here that has decent equipment (most people/bars/restaurants down here don’t). This service wants to be able to allow just your laptop to connect from you boat. Some people it works OK for, others not. Probably limited by the TX of the individual laptop card I would bet (as you described). With the we have been able to connect to this service from about 4 (nautical) miles offshore. With less fancy equipment being used onshore (a belkin or Linksys home access point), we might get about a mile, but that’s about it. So, I would think that both the RX and TX are important, unless you know the access point is so powerful, in that case, I would agree the TX of the USB card would be the limiting factor. Out here in the boating world, we try to connect to anything we can basically, and have no control over what’s on shore, so my feeling is anything that can help the RX is going to make a difference also, but probably only a side by side test would be able to prove it.