Thanks, thats quite a lot of suggestions!
Unfortunately spotlight, stencils and projectionmaster share the same weakness which is that the size of the alpha/texture is dependent on the zoom level of the model. While working on the model I wont be able to keep that consistent.
The alphas in question are 4 complete sets of fonts which is why PRS matters a great deal.
Turning all of them into 3D meshes for substracting actually has an edge over my carve brush approach but will take me days for the conversion i presume.
Also this introduces another problem which is that i need the topology to remain consistent because i want to animate the sculpting process using a displacement map thus i cant dynamesh unless I reproject onto my target topology for every substep i need to make for the animation.
Guess i keep redrawing the characters a lot to get them right.