Hi Al. I grow several varieties commercially down here in Cornwall and from experience, the hardiest in order are, A dealbata, A pravissima, A longifolia but I hope you realise just how fast they grow ??? A dealbata can easily grow 15ft in 3 yrs, as can longifolia ! One of the nicest is Acacia Baileyana (the Cootamunda Wattle) it has beautiful steely blue foliage, the most deliciously scented 'fluffy' yellow flowers (from Christmas onwards) and it can be kept relatively small. Regarding soil, the best variety for alkaline soil is A rhetinoides and whilst quick growing, it flowers several times during the year and also as a young tree (A. dealbata will take several years to flower) but its not the hardiest ! Prior to these recent cold winters, all the above have thrived down here but it depends on if this colder trend is now the 'norm' Even this year, whilst we only had one really cold spell, it was quite mild leading upto it and it took the newest growth out of my Acacias in the garden.
Depending where you are ? why not try growing one in a large tub that can be moved come winter, or be prepared to wrap the lower trunk/branches, at least this way, it will come again from the base !
regards, Lannerman.