Iris, I bought a lot of bottlebrush since my return to SC 5 years ago. Most of them turned out not to be cold hardy. I bought the bottlebrush you commented on at Simpson's Ace hardware here in town, and it's very cold hardy. Unfortunately, the garden manager didn't know the cultivar name, and the tag was only labeled "bottlebrush". She told me it came from a grower in Georgia who told her it was cold hardy to 5 degrees. This is a pic of another cold hardy bottlebrush that first blooms in April and again in late summer. The leaves are thinner, and the blooms are also a little different in size. I have yet another cold hardy variety that hasn't bloomed yet. It's leaves are very thin and the flowers aren't as showy. I noticed it being grown in a highway median in Bishopville, SC.
Hi Iris, I think the 2 bottlebrushes you commented on can be trained to grow into small trees. My oldest (2nd pic posted) was planted in Sept 08, so it survived winter 09 with very little root system. I bought and planted several of the other variety back in Feb. I plopped them in the ground and they were unfazed by temps in low 20's w/heavy frost - very cold hardy. I just passed a home today with two large bushes in yard - about 4' tall x 6' wide. The third variety(see pic) has only produced one bloom so far. As I posted earlier, it's leaves are very thin and it's flowers aren't as showy. It's growth habit is bushy - so much so that I have gathered the branches and tied with twine so when it does bloom, the effect will be more dramatic.
Don't buy Monrovia's dwarf bottlebrush. I've lost several to cold over the past 5 years, even though they're supposed to be cold hardy to zone 8. There's also a cold hardy yellow BB that I'd love to buy, but I've never seen it marketed here. Good luck!