On a T3 connection, Pro will let you download from 14 hosts compared to basic's 10. So there's the potential for faster downloads, if you're downloading from more hosts. But honestly, buying Pro's not going to send your download speeds through the roof

Pro also connects you to 5 ultrapeers, compared to basic's 3. So there's the potential for better search results. If you're searching for rarer files, it'll make more of a difference. If you only search for popular stuff, you probably won't see much of a change.

Lots of people see buying Pro more as a donation to continue LW's development