but what's driving me towards 3.2mm more than anything is the availability of pre made 'blade' bobbins in korea with an 1/8" 'blade' slot! (basicallly cutting bobbins on a dodgy homemade CNC takes forever
A friend of mine has had some success with 3D printed bobbins in his audio transformers. He had the prototypes made at Shapeways (from 3D models I made for him). Worth a look if you need complex shapes made in plastic as they only charge by weight and material (i.e. cheap-ish).

Bill