Thanks for sharing the interview with Lattner; that was quite interesting.

I agree with everything he said. However, I think you're either misinterpreting or glossing over the actual performance question. Lattner said:

The performance side of things I think is still up in the air because ARC certainly does introduce overhead. Some of that’s unavoidable, at least without lots of annotations in your code, but also I think that ARC is not done yet. A ton of energy’s been poured into research for garbage collection... That work really hasn’t been done for ARC yet, so really, I think there’s still a a big future ahead.

That's optimistic, but certainly not the same as saying there are no scenarios in which GC has performance wins.