Your network connection and your download speeds are different things.
The network is only used for searches and connection requests.
Downloading doesn't take place over the network
The actual downloading is a direct connection between computers.
So download speed are affected by a lot of factors.
e.g. You have a state of the art connection, and you want a file from me but I happen to live in Bongobongoland and have a 28K modem.
The speed you are going to get from me would not be spectacular.
There are hoever ways of getting the max out of Limewire.
Read
this for starters