philinacoma on the money there.
Take my area for example. Messmate (Eucalyptus Obliqua) usually has a decent flowering every second year. In 2007 it flowered the best it has in years and gave a very strong honey flow until it rained, and that killed the flow. Most commercial beekeepers didn't except it to finish that quickly. Its important to them if they are moving off something like yelllow box which is pollen deficient and they need something with excellent pollen to rejuvenate colonies heading into winter, and help prevent EFB in the spring. Last year, the extreme dry conditions put the messmate under too much stress to bud well, and then most of it was burnt out! So there are many factors affecting how much a Eucalypt will yield. Also, if you are growing them, when will they be mature and flower? As for actual figures on potential yield per tree or per hectare I can't help you.
However, not all is lost. I know commercial beekeepers who grow spotted gum on their wintering sites, as it usually provides some nectar and pollen over winter.
If you can get hold of the book honey flora of victoria, published by DPI some years ago that should help you. It contains more details specific to beekeepers than publications such as Brooker & Kleinig and Costamens.
What are you thinking about doing?