Seconded.
Personality also more noticeable if you spend a lot of time with them. Having said that, even among heritage breeds there are 'general trends' in personality, like Andalusian being more flighty/aloof, RIRs known as more dominant towards many other breeds.
I have not had a barred Plymouth Rock, but have a white PR crossed with Maran, and she is quite a good layer (I had intended to get a "white rock" this time, but none available). I had short listed RIR, but decided against due to the reputation being too bossy with the other breeds.
As a very general guide (IMO) it seems that the rounder, plumper birds are a bit more chilled and friendlier, and the skinner birds tend to be either more flighty / dominant / aloof. Also, lighter (skinnier) types tend to escape over fences a lot more. Hence, I go for the plump girls. This new batch of pullets - Columbian Wyandotte, Gold Pencilled Wyandotte and a Buff Orphington. I actually wanted a Silver Laced Wyandotte, but supply is an issue at the moment.
The Buff Orphington probably similar in personality to your Australorp (which has orphington in its pedigree). The only downside to the BO, the reputation for getting broody (but honestly, even the less broody breeds still go broody when the mood takes them - have a 'broody breaker' cage ready to be deployed in a nice cool, shady spot).