Just so you know, I am impressed by the depth you've delved into with JSON parsing and dumping. It looks like a lot of time and effort went into the analysis.
Merged. Didn't seem to make much difference though. Results for the original Oj parser are pretty close to the core json now. I'll have to update the README for Oj. It's a bit stale. The new Oj::Parser is still much faster if not restricted to the current Rails environment.