They are about 10x slower than hash- or array-based objects under average use

Agree with everything apart from this one, which doesn't match my experiences at all.

My inside out classes are within a gnat's whisker of being as fast as plain hash-based objects wherever I've used them, and the slowest inside-out object framework that I've come across (Class::Std) is only a bit over twice as slow when I've benchmarked it.