Hope this helps!
I would consider functionality into the equation as well. In the case of a fire, the only exit is... the spiral staircase. It might look great but imagine yourself as a 33 year old mother(or father), 2 children 3 and 7(it's 1AM), the only way to exit, is that spiral staircase. That's when resale comes to mind... one day you may want to sell and that couple walks through. Pregnant with second child. They look at that cool spiral staircase. One of their thoughts may be, "what's it going to cost to replace that?"
Just a thought... sometimes convention is good. Just my two cents.
Good luck in your thought process and research.
As Bev mentioned a reputable licensed contractor should be able to answer that for you, or if you want to get a preliminary idea you can go down to the building department. We do our own projects and work with several good contractors - if you'd like some referrals send me an email to firstname.lastname@example.org.
Lance King/Owner-Managing Broker