Sure, let me amend it to "i'm suspicious of any significant performance improvement in as system where performance actually matters, and has existed in a state where performance matters for a long time".

I'll believe you if you say 0.5% improvement, I'll believe you if you say 10,000% improvement, but 10%? That's fishy.

That's a different case. Corporate code is never optimized for performance. Performance as a factor doesn't play any factor.