@scotthomer - exactly as I thought. Amount of geo you have on the edges of the plaster is really good, as it is quite hard to tell what you have made there, hence why I asked. :)
With all those techniques (except the purely Z Brush one) I still seem to get nasty artefacts on most fonts. I have to go in and manually edit the polys, which can take 1-5 minutes per letter, but gives you more control in the end anyway. But if you're only going to see the letters from quite far away then these methods…