"Although STL can be sent to you CAm package and machined, it will be linear at some type of resolution."

With the exception of some high end machining software like Delcam, very few 3D cam packages send anything other than linear data to the CNC machine. Sure, a CAM package may import a nurbs model, but most likely its not sending spline coordinates in G-code to the machine. So starting with a polygonal model is somewhat irrelevant if the polys are small enough so they won't be seen in the finished piece. And that, of course, is also related to the material, tool size, feed rate, spindle speed, etc.