The differences between Basic & Pro are really rather subtle. Pro is good for those seeking the less common files in searches. With 2 extra peers it connects to & an internal improvement in search it can find a little extra.
As for downloading, basic connects to a maximum of 8 hosts per file compared to Pro's 10. So arguably should be able to get slightly faster downloads. But many people say they don't notice any difference at all so it's up to the particular person's findings.