I'm thinking about adding BSP support to my game but I've been playing around with Gtk Radiant and I'm not sure it can actually do everything I need it to. I was trying to create a spiral staircase but when I tried to move vertices on a brush it would move other vertices so that I was unable to make it look right. I'm starting to wonder if this is worth my time. Is Gtk Radiant suitable for making levels for my game?

Also is there a standard API for loading BSP files? Preferably Quake 4 and Doom 3 BSP files.