You're right, they are one and the same plant. It usually does survive perfectly well, specially in the south, but your problem is you want them up obelisks, which presumably are not going to be in the lee of a wall or fence, but fully exposed to the elements. It's usual to plant these up against a wall in a sheltered spot - if your obelisks are in a sheltered, south facing garden, you might get away with it.

Thank you Bamboo - unfortunately the obelisks will be fully exposed so I guess that I'll have to find another plant! any suggestions??!!

Can't think of anything that would look as good year round as Trachleospermum, unfortunately. Mind, this plant does eventually get quite large, so am not sure that growing on an obelisk is a good idea anyway. If the obelisks are attractive, why not consider late flowering Clematis, those in the viticelli/jackmanii group - you could cut all the growth down to about 6 inches end of October, early November so you weren't looking at dead stems all winter (these would normally be cut down by mid Feb the following year, but if you did it early November, the plants would be fine nonetheless).

Thanks Bamboo - I was hoping for something evergreen so perhaps I'd better settle for ivy!!