Will the data from $b->[0] be returned faster than that from $a->{'High'}? What if I write proper accessors?, i.e. $b->getLeft() versus $a->getHigh Is there a difference? Big? Small?

Personally I wouldn't care too much. But that's just me. What I keep hearing around is that micro-optimizations are rarely worth the effort. Then I have a limited experience in this sense, but it all tends to support such claims.