Can't really tell Kent, small pic. I usually like to make the cut early so it can heal before it gets cold here, if your weather is such that you will not experience cold, damp winter then it should be okay for a while. It does look a little like Cereus peruvianus, but I wouldn't make a tag on my word. Have you looked at http://www.columnar-cacti.org/ ? Nice site for all Cerei.
Dan
Lincoln, NE USDA 5

As long as you keep any exposed wound undercover and away from moisture you should be OK. If you do decide to cut it just keep it dry and then replant in mid-Spring to give it a chance. I live in Melbourne and our Winters are quite cold and wet, and I definitely would never try to reroot a plant at that time of year.

I agree with cactusdan, and think its likely to be a peruvianus. It's definitely one of the more common columnar cacti down here.

Thanks Dan & Danny. I think you are right its probably a peruvianus, although several look similar, such as Cereus validus but these may not be common here. I'll keep it dry and then if it doesnt take I'll slice it off and dry for spring.I read on the net that peruvianus are being trialled as a fruit export crop inthe Israeli desert. Ill just be happy if mine lives.

thanks

Kent, Melbourne, Australia.