As Julian has said, the 54Mbps is the rate at which data will transfer between computers or over the network.
In older machines the NIC may only be g instead of the n of later more standard machines, but we now also have ac which is much faster.
However, both the router and computers must have ac adapters, although they are backward compatible with b/g/n.
The other thing is that ac routers broadcast on the 5GHz band which ac requires, but the downside of that is that the wireless range of 5GHz is less than that of 2.4GHz.
2.4GHz will travel through walls whereas 5GHz bounces off them in what is known as the splatter effect - but I digress
The wireless NICs in my laptops are n and are capable of up to 300Mbps but because older laptops only had a mini NIC, that would be reduced to 150Mbps.
Desktop PCs have a full card in them so they will be able to achieve the 300Mbps.
For LAN, this can either be up to 100Mbps where the LAN adapter is a Family Controller (10/100), but when the computer has a GBE LAN adapter (10/100/1000) and the router has a Gigabit port, then that data transfer speed will be up to 1GB.
However, when transferring data between a machine with a n NIC onto a machine with a g NIC (or vice versa), the transfer speed will be restricted to the lowest which in this case will be the 54Mbps - this can be reduced further depending on the distance between machines and router and is why data transfer would probably best be done when the computers are wired.
My broadband download speed is approx. 6.7meg, so you can see there is no correlation between that and the data transfer speed.
