If by chance your speed is affected by your ISP in anyway, then Pro will not advantage you...
If you like looking for rarer files Pro will advantage you, it will do this because you will hook up to 5 Ultrapeers and download from up to 10 hosts, so in a way the more hosts you can connect to, can improve speed. It also depends on the speed of the hosts you are downloading from...
There are so many factors to configuring your LW properly...
If you do decide to get PRO you get 6 months of free updates and then you get a discount if you want a further 6 months and so on..You are not able to get refunds if you are not happy with it.....
Limewire is not run by servers at all it is just a program that links you to computers all over the world that use P2P....
Also if you choose to purchase Pro make sure you get it from the official site only
http://www.limewire.com