I have a HO 4-8-4 that doesn't even like 24" radius, almost 2x bigger than the curve mentioned above. If NickB is in N scale he should be ok. It is always best to go with the biggest curve possible even if it means leaving out some track. Most model railroaders try to do too much in a given space. I am building some modules and keep reminding myself that in HO a 2ft x 4ft module is only slightly larger than an American football field.
Here is a link to a photo of my next up for construction module. It is BN jct in Hillsboro, OR. The yellow lines are outlines of the 3 modules it will take to build it in a way it will fit in my Civic. The ends are 24" wide and the curve is 42" radius. In HO, the real life the curve is about a 48" radius and it looks pretty sharp standing on the ground next to it.
http://members.trainorders.com/pmack/temp/BNjct2.jpg
Thanks for letting me go off about one thing that bugs me, overly sharp curves,
Paul Mack
Hillsboro, OR
http://members.trainorders.com/pmack/train.htm