I have to agree with the barrel choices: WOA, Pac-Nor, and for a bit more Krieger.

You can build your own upper assembly fairly easily, you'll need an upper receiver wrench and a barrel nut wrech though (about $75 worth of tools). Only 'disadvantage' if you call it that, is that you won't be able to pin your FSB to your barrel, but it sounds like you are interested in building a preceision rifle where pinning is a no-no anyhow.

For good info on building for precision, check out the book "The Competitive AR-15" by Glen Zediker.