But more results isn't always good. Especially given that LimeWire can't filter ports.

An Ultrapeer connection blinds the client to the realities of possible or impossible connections. With 0.6 connections a greater percentage (still not all, but MUCH more) of the queryhits you get are from hosts that you can actually connect to, because obviously if you got the queryhit you can exchange data with that host. Funneling everything in and out via an UP means that more queryhits are returned, but most of the leaves of an average Ultrapeer are inaccesible to me. Getting queryhits bounced off of an Ultrapeer only means that both the host in question and myself can connect to the Ultrapeer. The fact that the Ultrapeer allows me to get queryhits from these hosts is of little consequence in terms of being able to access the hosts themselves, because the actual business of requests and transfers is handled directly between me and the host in question.

With a 0.6 connection, a much greater percentage of my search horizon is made up of hosts I can get to. I have fewer responses, but most of the queryhits I lose vs. an ultrapeer setup represent hosts I could not get to anyway.

In short, a Ultrapeer gives me hits from anything the Ultrapeer can connect to. In a perfect world, I would be able to connect to all of them as well. But I can't. A 0.6 connection gives a more accurate description of files available to me.