Always remember size is everything
If you get into OC6 races, especially change races (not likely for chaos though, have to swim), then you should have a blade close to what all the paddlers in your boat will have. If the majority have a 51.5 or 52 inch blade then get something like that. That will save people from getting in your seat and having a short paddle and that could screw them up somewhat.
Choose a 51.5 or 52, I have a 52 myself and I am about the same height as you are.