you won't see much difference. The searches go a little farther, the downloads can come from a few more sources, and you connect to a couple more ultrapeers when you are a leaf.

However, the LW folks can tweak the settings from version to version: they really just try to give the Pro supporters a bit more without crippling the Free or the network.

IMHO, I keep supporting Pro because it's one way to help support the work the developers and volunteers do. I hate leeching, so Pro helps.