Thanks for your experience, but the passively cooled 12" Macbook is really a different thing. Basically, it isn't a 2.5 GHz CPU that throttles, but a 1.1 GHz CPU which can boost itself for a very short time, and the it runs into thermal limit and returns to a 1.1 GHz sustained performance.

And on hot day, that boost might last 30 seconds and then that's it.