Some positive feedback FYI.
I updated from 3.6.15 to 4.2.6. I have noticed 4.2.6 connections are much more stable than 3.6.15.
3.6.15 used to try and establish 4 ultrapeer connections, but if it ever dropped to 3, which was quite often, I noticed a large drop in search and download success.
4.2.6 almost always manages to keep 3 connections up, which seems to give good search and download results.