We ran another test job on a Roland EGX 600 to see how it coped with engraving slate.
The results were very good and the sign shown below that measures 350mm x 250mm was engraved using a 100 degree included angle, top loading carbide cutter in approximately 1 hour . As this was our first attempt into slate we ran the feedrates on the cautious side (10mm / sec), and this could possibly have been at least 30% - 50% faster.
Just need to work out out how to take better pictures - any advice would be appreciated.