Definitely not Acacia melanoxylon. That species has cladodes
(flattened leaf stems that function as leaves) at maturity and the
bipinnate leaves are only present on very young plants. It might just
be Acacia decurrens (Green Wattle), but the flowering period and pale
flowers suggest otherwise. Trouble is, normal dealbata 'Subalpina'
has the characteristic silvery leaves of the species and your are
green, as are those of the Paignton tree. I'll have a chat with a few
mates in Oz.