>I would certainly prefer it if PyPy was 100% compatible with the CPython C API even if it was at 80% (maybe even 60%) of the CPython C API speed because then I don't even have to think. I'd be using PyPy because it's faster overall and I can do the analyses I want faster.

While part of me agrees with this, if PyPy starts sacrificing performance for CPython compatibility then pretty soon it'll degenerate into CPython.