Over the past week I've made some great progress on my OpenSim experiment. For starters, I've got my server configured in Grid mode, and I have all four of the main servers running on SQL Server. This did require a bit of development - the inventory server was quite broken for SQL Server, so James and I fixed the code and submitted a patch, but the good news is that this means it'll be in a better state for the rest of you from now on.
If you're committed to switching from SQLite as much as possible then I would recommend...