I read this even before going to work this morning, and after all this additional time to think about it, and as literate as I'd like to believe I am, my best response remains "Sweet!" However much luck may have contributed to a decent OC and the unlock, any change I might come up with would be niggling. I can't even grouse about the budget too much, as 1) prices were different, and 2) cuts in non-core items (e.g. case and HDD) would bring it down.
I do like the idea of finding a way to add upgradability to the SBM, or simply upgrades; e.g. start with three old Dells and throw $100, $200, and $500 at them, and see how much you can improve each one. No rules other than a strict budget; specifically mobo replacement IS allowed.
I also hope the excellent results here mean we will never again see a miserable e5x00 in another budget build.